--- a/layout/style/ServoStyleSheet.cpp
+++ b/layout/style/ServoStyleSheet.cpp
@@ -20,402 +20,9 @@
 
 
 #include "mozAutoDocUpdate.h"
 
 using namespace mozilla::dom;
 
 namespace mozilla {
 
-// -------------------------------
-// CSS Style Sheet Inner Data Container
-//
-
-void
-ServoStyleSheet::BuildChildListAfterInnerClone()
-{
-  MOZ_ASSERT(Inner()->mSheets.Length() == 1, "Should've just cloned");
-  MOZ_ASSERT(Inner()->mSheets[0] == this);
-  MOZ_ASSERT(!Inner()->mFirstChild);
-
-  auto* contents = Inner()->mContents.get();
-  RefPtr<ServoCssRules> rules =
-    Servo_StyleSheet_GetRules(contents).Consume();
-
-  uint32_t index = 0;
-  while (true) {
-    uint32_t line, column; // Actually unused.
-    RefPtr<RawServoImportRule> import =
-      Servo_CssRules_GetImportRuleAt(rules, index, &line, &column).Consume();
-    if (!import) {
-      // Note that only @charset rules come before @import rules, and @charset
-      // rules are parsed but skipped, so we can stop iterating as soon as we
-      // find something that isn't an @import rule.
-      break;
-    }
-    auto* sheet =
-      const_cast<ServoStyleSheet*>(Servo_ImportRule_GetSheet(import));
-    MOZ_ASSERT(sheet);
-    PrependStyleSheetSilently(sheet);
-    index++;
-  }
-}
-
-already_AddRefed<ServoStyleSheet>
-ServoStyleSheet::CreateEmptyChildSheet(
-    already_AddRefed<dom::MediaList> aMediaList) const
-{
-  RefPtr<ServoStyleSheet> child =
-    new ServoStyleSheet(
-        ParsingMode(),
-        CORSMode::CORS_NONE,
-        GetReferrerPolicy(),
-        SRIMetadata());
-
-  child->mMedia = aMediaList;
-  return child.forget();
-}
-
-MOZ_DEFINE_MALLOC_SIZE_OF(ServoStyleSheetMallocSizeOf)
-MOZ_DEFINE_MALLOC_ENCLOSING_SIZE_OF(ServoStyleSheetMallocEnclosingSizeOf)
-
-// We disable parallel stylesheet parsing if any of the following three
-// conditions hold:
-//
-// (1) The pref is off.
-// (2) The browser is recording CSS errors (which parallel parsing can't handle).
-// (3) The stylesheet is a chrome stylesheet, since those can use -moz-bool-pref,
-//     which needs to access the pref service, which is not threadsafe.
-static bool
-AllowParallelParse(css::Loader* aLoader, nsIURI* aSheetURI)
-{
-  // Check the pref.
-  if (!StaticPrefs::layout_css_parsing_parallel()) {
-    return false;
-  }
-
-  // If the browser is recording CSS errors, we need to use the sequential path
-  // because the parallel path doesn't support that.
-  nsIDocument* doc = aLoader->GetDocument();
-  if (doc && css::ErrorReporter::ShouldReportErrors(*doc)) {
-    return false;
-  }
-
-  // If this is a chrome stylesheet, it might use -moz-bool-pref, which needs to
-  // access the pref service, which is not thread-safe. We could probably expose
-  // the relevant booleans as thread-safe var caches if we needed to, but
-  // parsing chrome stylesheets in parallel is unlikely to be a win anyway.
-  //
-  // Note that UA stylesheets can also use -moz-bool-pref, but those are always
-  // parsed sync.
-  if (dom::IsChromeURI(aSheetURI)) {
-    return false;
-  }
-
-  return true;
-}
-
-RefPtr<StyleSheetParsePromise>
-ServoStyleSheet::ParseSheet(css::Loader* aLoader,
-                            const nsACString& aBytes,
-                            css::SheetLoadData* aLoadData)
-{
-  MOZ_ASSERT(aLoader);
-  MOZ_ASSERT(aLoadData);
-  MOZ_ASSERT(mParsePromise.IsEmpty());
-  RefPtr<StyleSheetParsePromise> p = mParsePromise.Ensure(__func__);
-  Inner()->mURLData =
-    new URLExtraData(GetBaseURI(), GetSheetURI(), Principal()); // RefPtr
-
-  if (!AllowParallelParse(aLoader, GetSheetURI())) {
-    RefPtr<RawServoStyleSheetContents> contents =
-      Servo_StyleSheet_FromUTF8Bytes(aLoader,
-                                     this,
-                                     aLoadData,
-                                     &aBytes,
-                                     mParsingMode,
-                                     Inner()->mURLData,
-                                     aLoadData->mLineNumber,
-                                     aLoader->GetCompatibilityMode(),
-                                     /* reusable_sheets = */ nullptr)
-      .Consume();
-    FinishAsyncParse(contents.forget());
-  } else {
-    RefPtr<css::SheetLoadDataHolder> loadDataHolder =
-      new css::SheetLoadDataHolder(__func__, aLoadData);
-    Servo_StyleSheet_FromUTF8BytesAsync(loadDataHolder,
-                                        Inner()->mURLData,
-                                        &aBytes,
-                                        mParsingMode,
-                                        aLoadData->mLineNumber,
-                                        aLoader->GetCompatibilityMode());
-  }
-
-  return Move(p);
-}
-
-void
-ServoStyleSheet::FinishAsyncParse(already_AddRefed<RawServoStyleSheetContents> aSheetContents)
-{
-  MOZ_ASSERT(NS_IsMainThread());
-  MOZ_ASSERT(!mParsePromise.IsEmpty());
-  Inner()->mContents = aSheetContents;
-  FinishParse();
-  mParsePromise.Resolve(true, __func__);
-}
-
-
-void
-ServoStyleSheet::ParseSheetSync(css::Loader* aLoader,
-                                const nsACString& aBytes,
-                                css::SheetLoadData* aLoadData,
-                                uint32_t aLineNumber,
-                                css::LoaderReusableStyleSheets* aReusableSheets)
-{
-  nsCompatibility compatMode =
-    aLoader ? aLoader->GetCompatibilityMode() : eCompatibility_FullStandards;
-
-  Inner()->mURLData = new URLExtraData(GetBaseURI(), GetSheetURI(), Principal()); // RefPtr
-  Inner()->mContents = Servo_StyleSheet_FromUTF8Bytes(aLoader,
-                                                      this,
-                                                      aLoadData,
-                                                      &aBytes,
-                                                      mParsingMode,
-                                                      Inner()->mURLData,
-                                                      aLineNumber,
-                                                      compatMode,
-                                                      aReusableSheets)
-                         .Consume();
-
-  FinishParse();
-}
-
-void
-ServoStyleSheet::FinishParse()
-{
-  nsString sourceMapURL;
-  Servo_StyleSheet_GetSourceMapURL(Inner()->mContents, &sourceMapURL);
-  SetSourceMapURLFromComment(sourceMapURL);
-
-  nsString sourceURL;
-  Servo_StyleSheet_GetSourceURL(Inner()->mContents, &sourceURL);
-  SetSourceURL(sourceURL);
-}
-
-nsresult
-ServoStyleSheet::ReparseSheet(const nsAString& aInput)
-{
-  if (!mInner->mComplete) {
-    return NS_ERROR_DOM_INVALID_ACCESS_ERR;
-  }
-
-  // Hold strong ref to the CSSLoader in case the document update
-  // kills the document
-  RefPtr<css::Loader> loader;
-  if (mDocument) {
-    loader = mDocument->CSSLoader();
-    NS_ASSERTION(loader, "Document with no CSS loader!");
-  } else {
-    loader = new css::Loader;
-  }
-
-  mozAutoDocUpdate updateBatch(mDocument, UPDATE_STYLE, true);
-
-  WillDirty();
-
-  // cache child sheets to reuse
-  css::LoaderReusableStyleSheets reusableSheets;
-  for (StyleSheet* child = GetFirstChild(); child; child = child->mNext) {
-    if (child->GetOriginalURI()) {
-      reusableSheets.AddReusableSheet(child);
-    }
-  }
-
-  // clean up child sheets list
-  for (StyleSheet* child = GetFirstChild(); child; ) {
-    StyleSheet* next = child->mNext;
-    child->mParent = nullptr;
-    child->SetAssociatedDocument(nullptr, NotOwnedByDocument);
-    child->mNext = nullptr;
-    child = next;
-  }
-  Inner()->mFirstChild = nullptr;
-
-  uint32_t lineNumber = 1;
-  if (mOwningNode) {
-    nsCOMPtr<nsIStyleSheetLinkingElement> link = do_QueryInterface(mOwningNode);
-    if (link) {
-      lineNumber = link->GetLineNumber();
-    }
-  }
-
-  // Notify to the stylesets about the old rules going away.
-  {
-    ServoCSSRuleList* ruleList = GetCssRulesInternal();
-    MOZ_ASSERT(ruleList);
-
-    uint32_t ruleCount = ruleList->Length();
-    for (uint32_t i = 0; i < ruleCount; ++i) {
-      css::Rule* rule = ruleList->GetRule(i);
-      MOZ_ASSERT(rule);
-      if (rule->Type() == CSSRuleBinding::IMPORT_RULE &&
-          RuleHasPendingChildSheet(rule)) {
-        continue; // notify when loaded (see StyleSheetLoaded)
-      }
-      RuleRemoved(*rule);
-    }
-  }
-
-  DropRuleList();
-
-  ParseSheetSync(loader,
-                 NS_ConvertUTF16toUTF8(aInput),
-                 /* aLoadData = */ nullptr,
-                 lineNumber,
-                 &reusableSheets);
-
-  // Notify the stylesets about the new rules.
-  {
-    // Get the rule list (which will need to be regenerated after ParseSheet).
-    ServoCSSRuleList* ruleList = GetCssRulesInternal();
-    MOZ_ASSERT(ruleList);
-
-    uint32_t ruleCount = ruleList->Length();
-    for (uint32_t i = 0; i < ruleCount; ++i) {
-      css::Rule* rule = ruleList->GetRule(i);
-      MOZ_ASSERT(rule);
-      if (rule->Type() == CSSRuleBinding::IMPORT_RULE &&
-          RuleHasPendingChildSheet(rule)) {
-        continue; // notify when loaded (see StyleSheetLoaded)
-      }
-
-      RuleAdded(*rule);
-    }
-  }
-
-  // Our rules are no longer considered modified.
-  ClearModifiedRules();
-
-  return NS_OK;
-}
-
-// nsICSSLoaderObserver implementation
-NS_IMETHODIMP
-ServoStyleSheet::StyleSheetLoaded(StyleSheet* aSheet,
-                                  bool aWasAlternate,
-                                  nsresult aStatus)
-{
-  if (!aSheet->GetParentSheet()) {
-    return NS_OK; // ignore if sheet has been detached already
-  }
-  NS_ASSERTION(this == aSheet->GetParentSheet(),
-               "We are being notified of a sheet load for a sheet that is not our child!");
-
-  if (NS_SUCCEEDED(aStatus)) {
-    mozAutoDocUpdate updateBatch(mDocument, UPDATE_STYLE, true);
-    RuleAdded(*aSheet->GetOwnerRule());
-  }
-
-  return NS_OK;
-}
-
-void
-ServoStyleSheet::DropRuleList()
-{
-  if (mRuleList) {
-    mRuleList->DropReference();
-    mRuleList = nullptr;
-  }
-}
-
-already_AddRefed<StyleSheet>
-ServoStyleSheet::Clone(StyleSheet* aCloneParent,
-                       dom::CSSImportRule* aCloneOwnerRule,
-                       nsIDocument* aCloneDocument,
-                       nsINode* aCloneOwningNode) const
-{
-  RefPtr<StyleSheet> clone = new ServoStyleSheet(*this,
-    static_cast<ServoStyleSheet*>(aCloneParent),
-    aCloneOwnerRule,
-    aCloneDocument,
-    aCloneOwningNode);
-  return clone.forget();
-}
-
-ServoCSSRuleList*
-ServoStyleSheet::GetCssRulesInternal()
-{
-  if (!mRuleList) {
-    EnsureUniqueInner();
-
-    RefPtr<ServoCssRules> rawRules =
-      Servo_StyleSheet_GetRules(Inner()->mContents).Consume();
-    MOZ_ASSERT(rawRules);
-    mRuleList = new ServoCSSRuleList(rawRules.forget(), this);
-  }
-  return mRuleList;
-}
-
-uint32_t
-ServoStyleSheet::InsertRuleInternal(const nsAString& aRule,
-                                    uint32_t aIndex, ErrorResult& aRv)
-{
-  // Ensure mRuleList is constructed.
-  GetCssRulesInternal();
-
-  mozAutoDocUpdate updateBatch(mDocument, UPDATE_STYLE, true);
-  aRv = mRuleList->InsertRule(aRule, aIndex);
-  if (aRv.Failed()) {
-    return 0;
-  }
-
-  // XXX We may not want to get the rule when stylesheet change event
-  // is not enabled.
-  css::Rule* rule = mRuleList->GetRule(aIndex);
-  if (rule->Type() != CSSRuleBinding::IMPORT_RULE ||
-      !RuleHasPendingChildSheet(rule)) {
-    RuleAdded(*rule);
-  }
-
-  return aIndex;
-}
-
-void
-ServoStyleSheet::DeleteRuleInternal(uint32_t aIndex, ErrorResult& aRv)
-{
-  // Ensure mRuleList is constructed.
-  GetCssRulesInternal();
-  if (aIndex >= mRuleList->Length()) {
-    aRv.Throw(NS_ERROR_DOM_INDEX_SIZE_ERR);
-    return;
-  }
-
-  mozAutoDocUpdate updateBatch(mDocument, UPDATE_STYLE, true);
-  // Hold a strong ref to the rule so it doesn't die when we remove it
-  // from the list. XXX We may not want to hold it if stylesheet change
-  // event is not enabled.
-  RefPtr<css::Rule> rule = mRuleList->GetRule(aIndex);
-  aRv = mRuleList->DeleteRule(aIndex);
-  MOZ_ASSERT(!aRv.ErrorCodeIs(NS_ERROR_DOM_INDEX_SIZE_ERR),
-             "IndexSizeError should have been handled earlier");
-  if (!aRv.Failed()) {
-    RuleRemoved(*rule);
-  }
-}
-
-nsresult
-ServoStyleSheet::InsertRuleIntoGroupInternal(const nsAString& aRule,
-                                             css::GroupRule* aGroup,
-                                             uint32_t aIndex)
-{
-  auto rules = static_cast<ServoCSSRuleList*>(aGroup->CssRules());
-  MOZ_ASSERT(rules->GetParentRule() == aGroup);
-  return rules->InsertRule(aRule, aIndex);
-}
-
-OriginFlags
-ServoStyleSheet::GetOrigin()
-{
-  return static_cast<OriginFlags>(
-    Servo_StyleSheet_GetOrigin(Inner()->mContents));
-}
-
 } // namespace mozilla

--- a/layout/style/StyleSheet.cpp
+++ b/layout/style/StyleSheet.cpp
@@ -11,17 +11,16 @@
 #include "mozilla/dom/CSSImportRule.h"
 #include "mozilla/dom/CSSRuleList.h"
 #include "mozilla/dom/Element.h"
 #include "mozilla/dom/MediaList.h"
 #include "mozilla/dom/ShadowRoot.h"
 #include "mozilla/dom/ShadowRootBinding.h"
 #include "mozilla/ServoCSSRuleList.h"
 #include "mozilla/ServoStyleSet.h"
-#include "mozilla/ServoStyleSheet.h"
 #include "mozilla/StyleSheetInlines.h"
 
 #include "mozAutoDocUpdate.h"
 #include "NullPrincipal.h"
 
 namespace mozilla {
 
 StyleSheet::StyleSheet(css::SheetParsingMode aParsingMode,
@@ -301,16 +300,19 @@ StyleSheetInfo::~StyleSheetInfo()
 }
 
 StyleSheetInfo*
 StyleSheetInfo::CloneFor(StyleSheet* aPrimarySheet)
 {
   return new StyleSheetInfo(*this, aPrimarySheet);
 }
 
+MOZ_DEFINE_MALLOC_SIZE_OF(ServoStyleSheetMallocSizeOf)
+MOZ_DEFINE_MALLOC_ENCLOSING_SIZE_OF(ServoStyleSheetMallocEnclosingSizeOf)
+
 size_t
 StyleSheetInfo::SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const
 {
   size_t n = aMallocSizeOf(this);
   n += Servo_StyleSheet_SizeOfIncludingThis(
       ServoStyleSheetMallocSizeOf,
       ServoStyleSheetMallocEnclosingSizeOf,
       mContents);
@@ -898,9 +900,396 @@ StyleSheet::RuleHasPendingChildSheet(css
   MOZ_ASSERT(aRule->Type() == dom::CSSRuleBinding::IMPORT_RULE);
   auto rule = static_cast<dom::CSSImportRule*>(aRule);
   if (StyleSheet* childSheet = rule->GetStyleSheet()) {
     return !childSheet->IsComplete();
   }
   return false;
 }
 
+void
+StyleSheet::BuildChildListAfterInnerClone()
+{
+  MOZ_ASSERT(Inner()->mSheets.Length() == 1, "Should've just cloned");
+  MOZ_ASSERT(Inner()->mSheets[0] == this);
+  MOZ_ASSERT(!Inner()->mFirstChild);
+
+  auto* contents = Inner()->mContents.get();
+  RefPtr<ServoCssRules> rules =
+    Servo_StyleSheet_GetRules(contents).Consume();
+
+  uint32_t index = 0;
+  while (true) {
+    uint32_t line, column; // Actually unused.
+    RefPtr<RawServoImportRule> import =
+      Servo_CssRules_GetImportRuleAt(rules, index, &line, &column).Consume();
+    if (!import) {
+      // Note that only @charset rules come before @import rules, and @charset
+      // rules are parsed but skipped, so we can stop iterating as soon as we
+      // find something that isn't an @import rule.
+      break;
+    }
+    auto* sheet =
+      const_cast<StyleSheet*>(Servo_ImportRule_GetSheet(import));
+    MOZ_ASSERT(sheet);
+    PrependStyleSheetSilently(sheet);
+    index++;
+  }
+}
+
+already_AddRefed<StyleSheet>
+StyleSheet::CreateEmptyChildSheet(
+    already_AddRefed<dom::MediaList> aMediaList) const
+{
+  RefPtr<StyleSheet> child =
+    new StyleSheet(ParsingMode(),
+                   CORSMode::CORS_NONE,
+                   GetReferrerPolicy(),
+                   SRIMetadata());
+
+  child->mMedia = aMediaList;
+  return child.forget();
+}
+
+// We disable parallel stylesheet parsing if any of the following three
+// conditions hold:
+//
+// (1) The pref is off.
+// (2) The browser is recording CSS errors (which parallel parsing can't handle).
+// (3) The stylesheet is a chrome stylesheet, since those can use -moz-bool-pref,
+//     which needs to access the pref service, which is not threadsafe.
+static bool
+AllowParallelParse(css::Loader* aLoader, nsIURI* aSheetURI)
+{
+  // Check the pref.
+  if (!StaticPrefs::layout_css_parsing_parallel()) {
+    return false;
+  }
+
+  // If the browser is recording CSS errors, we need to use the sequential path
+  // because the parallel path doesn't support that.
+  nsIDocument* doc = aLoader->GetDocument();
+  if (doc && css::ErrorReporter::ShouldReportErrors(*doc)) {
+    return false;
+  }
+
+  // If this is a chrome stylesheet, it might use -moz-bool-pref, which needs to
+  // access the pref service, which is not thread-safe. We could probably expose
+  // the relevant booleans as thread-safe var caches if we needed to, but
+  // parsing chrome stylesheets in parallel is unlikely to be a win anyway.
+  //
+  // Note that UA stylesheets can also use -moz-bool-pref, but those are always
+  // parsed sync.
+  if (dom::IsChromeURI(aSheetURI)) {
+    return false;
+  }
+
+  return true;
+}
+
+RefPtr<StyleSheetParsePromise>
+StyleSheet::ParseSheet(css::Loader* aLoader,
+                            const nsACString& aBytes,
+                            css::SheetLoadData* aLoadData)
+{
+  MOZ_ASSERT(aLoader);
+  MOZ_ASSERT(aLoadData);
+  MOZ_ASSERT(mParsePromise.IsEmpty());
+  RefPtr<StyleSheetParsePromise> p = mParsePromise.Ensure(__func__);
+  Inner()->mURLData =
+    new URLExtraData(GetBaseURI(), GetSheetURI(), Principal()); // RefPtr
+
+  if (!AllowParallelParse(aLoader, GetSheetURI())) {
+    RefPtr<RawServoStyleSheetContents> contents =
+      Servo_StyleSheet_FromUTF8Bytes(aLoader,
+                                     this,
+                                     aLoadData,
+                                     &aBytes,
+                                     mParsingMode,
+                                     Inner()->mURLData,
+                                     aLoadData->mLineNumber,
+                                     aLoader->GetCompatibilityMode(),
+                                     /* reusable_sheets = */ nullptr)
+      .Consume();
+    FinishAsyncParse(contents.forget());
+  } else {
+    RefPtr<css::SheetLoadDataHolder> loadDataHolder =
+      new css::SheetLoadDataHolder(__func__, aLoadData);
+    Servo_StyleSheet_FromUTF8BytesAsync(loadDataHolder,
+                                        Inner()->mURLData,
+                                        &aBytes,
+                                        mParsingMode,
+                                        aLoadData->mLineNumber,
+                                        aLoader->GetCompatibilityMode());
+  }
+
+  return Move(p);
+}
+
+void
+StyleSheet::FinishAsyncParse(already_AddRefed<RawServoStyleSheetContents> aSheetContents)
+{
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(!mParsePromise.IsEmpty());
+  Inner()->mContents = aSheetContents;
+  FinishParse();
+  mParsePromise.Resolve(true, __func__);
+}
+
+
+void
+StyleSheet::ParseSheetSync(css::Loader* aLoader,
+                           const nsACString& aBytes,
+                           css::SheetLoadData* aLoadData,
+                           uint32_t aLineNumber,
+                           css::LoaderReusableStyleSheets* aReusableSheets)
+{
+  nsCompatibility compatMode =
+    aLoader ? aLoader->GetCompatibilityMode() : eCompatibility_FullStandards;
+
+  Inner()->mURLData = new URLExtraData(GetBaseURI(), GetSheetURI(), Principal()); // RefPtr
+  Inner()->mContents = Servo_StyleSheet_FromUTF8Bytes(aLoader,
+                                                      this,
+                                                      aLoadData,
+                                                      &aBytes,
+                                                      mParsingMode,
+                                                      Inner()->mURLData,
+                                                      aLineNumber,
+                                                      compatMode,
+                                                      aReusableSheets)
+                         .Consume();
+
+  FinishParse();
+}
+
+void
+StyleSheet::FinishParse()
+{
+  nsString sourceMapURL;
+  Servo_StyleSheet_GetSourceMapURL(Inner()->mContents, &sourceMapURL);
+  SetSourceMapURLFromComment(sourceMapURL);
+
+  nsString sourceURL;
+  Servo_StyleSheet_GetSourceURL(Inner()->mContents, &sourceURL);
+  SetSourceURL(sourceURL);
+}
+
+nsresult
+StyleSheet::ReparseSheet(const nsAString& aInput)
+{
+  if (!mInner->mComplete) {
+    return NS_ERROR_DOM_INVALID_ACCESS_ERR;
+  }
+
+  // Hold strong ref to the CSSLoader in case the document update
+  // kills the document
+  RefPtr<css::Loader> loader;
+  if (mDocument) {
+    loader = mDocument->CSSLoader();
+    NS_ASSERTION(loader, "Document with no CSS loader!");
+  } else {
+    loader = new css::Loader;
+  }
+
+  mozAutoDocUpdate updateBatch(mDocument, UPDATE_STYLE, true);
+
+  WillDirty();
+
+  // cache child sheets to reuse
+  css::LoaderReusableStyleSheets reusableSheets;
+  for (StyleSheet* child = GetFirstChild(); child; child = child->mNext) {
+    if (child->GetOriginalURI()) {
+      reusableSheets.AddReusableSheet(child);
+    }
+  }
+
+  // clean up child sheets list
+  for (StyleSheet* child = GetFirstChild(); child; ) {
+    StyleSheet* next = child->mNext;
+    child->mParent = nullptr;
+    child->SetAssociatedDocument(nullptr, NotOwnedByDocument);
+    child->mNext = nullptr;
+    child = next;
+  }
+  Inner()->mFirstChild = nullptr;
+
+  uint32_t lineNumber = 1;
+  if (mOwningNode) {
+    nsCOMPtr<nsIStyleSheetLinkingElement> link = do_QueryInterface(mOwningNode);
+    if (link) {
+      lineNumber = link->GetLineNumber();
+    }
+  }
+
+  // Notify to the stylesets about the old rules going away.
+  {
+    ServoCSSRuleList* ruleList = GetCssRulesInternal();
+    MOZ_ASSERT(ruleList);
+
+    uint32_t ruleCount = ruleList->Length();
+    for (uint32_t i = 0; i < ruleCount; ++i) {
+      css::Rule* rule = ruleList->GetRule(i);
+      MOZ_ASSERT(rule);
+      if (rule->Type() == CSSRuleBinding::IMPORT_RULE &&
+          RuleHasPendingChildSheet(rule)) {
+        continue; // notify when loaded (see StyleSheetLoaded)
+      }
+      RuleRemoved(*rule);
+    }
+  }
+
+  DropRuleList();
+
+  ParseSheetSync(loader,
+                 NS_ConvertUTF16toUTF8(aInput),
+                 /* aLoadData = */ nullptr,
+                 lineNumber,
+                 &reusableSheets);
+
+  // Notify the stylesets about the new rules.
+  {
+    // Get the rule list (which will need to be regenerated after ParseSheet).
+    ServoCSSRuleList* ruleList = GetCssRulesInternal();
+    MOZ_ASSERT(ruleList);
+
+    uint32_t ruleCount = ruleList->Length();
+    for (uint32_t i = 0; i < ruleCount; ++i) {
+      css::Rule* rule = ruleList->GetRule(i);
+      MOZ_ASSERT(rule);
+      if (rule->Type() == CSSRuleBinding::IMPORT_RULE &&
+          RuleHasPendingChildSheet(rule)) {
+        continue; // notify when loaded (see StyleSheetLoaded)
+      }
+
+      RuleAdded(*rule);
+    }
+  }
+
+  // Our rules are no longer considered modified.
+  ClearModifiedRules();
+
+  return NS_OK;
+}
+
+// nsICSSLoaderObserver implementation
+NS_IMETHODIMP
+StyleSheet::StyleSheetLoaded(StyleSheet* aSheet,
+                             bool aWasAlternate,
+                             nsresult aStatus)
+{
+  if (!aSheet->GetParentSheet()) {
+    return NS_OK; // ignore if sheet has been detached already
+  }
+  NS_ASSERTION(this == aSheet->GetParentSheet(),
+               "We are being notified of a sheet load for a sheet that is not our child!");
+
+  if (NS_SUCCEEDED(aStatus)) {
+    mozAutoDocUpdate updateBatch(mDocument, UPDATE_STYLE, true);
+    RuleAdded(*aSheet->GetOwnerRule());
+  }
+
+  return NS_OK;
+}
+
+void
+StyleSheet::DropRuleList()
+{
+  if (mRuleList) {
+    mRuleList->DropReference();
+    mRuleList = nullptr;
+  }
+}
+
+already_AddRefed<StyleSheet>
+StyleSheet::Clone(StyleSheet* aCloneParent,
+                  dom::CSSImportRule* aCloneOwnerRule,
+                  nsIDocument* aCloneDocument,
+                  nsINode* aCloneOwningNode) const
+{
+  RefPtr<StyleSheet> clone =
+    new StyleSheet(*this,
+                   aCloneParent,
+                   aCloneOwnerRule,
+                   aCloneDocument,
+                   aCloneOwningNode);
+  return clone.forget();
+}
+
+ServoCSSRuleList*
+StyleSheet::GetCssRulesInternal()
+{
+  if (!mRuleList) {
+    EnsureUniqueInner();
+
+    RefPtr<ServoCssRules> rawRules =
+      Servo_StyleSheet_GetRules(Inner()->mContents).Consume();
+    MOZ_ASSERT(rawRules);
+    mRuleList = new ServoCSSRuleList(rawRules.forget(), this);
+  }
+  return mRuleList;
+}
+
+uint32_t
+StyleSheet::InsertRuleInternal(const nsAString& aRule,
+                               uint32_t aIndex,
+                               ErrorResult& aRv)
+{
+  // Ensure mRuleList is constructed.
+  GetCssRulesInternal();
+
+  mozAutoDocUpdate updateBatch(mDocument, UPDATE_STYLE, true);
+  aRv = mRuleList->InsertRule(aRule, aIndex);
+  if (aRv.Failed()) {
+    return 0;
+  }
+
+  // XXX We may not want to get the rule when stylesheet change event
+  // is not enabled.
+  css::Rule* rule = mRuleList->GetRule(aIndex);
+  if (rule->Type() != CSSRuleBinding::IMPORT_RULE ||
+      !RuleHasPendingChildSheet(rule)) {
+    RuleAdded(*rule);
+  }
+
+  return aIndex;
+}
+
+void
+StyleSheet::DeleteRuleInternal(uint32_t aIndex, ErrorResult& aRv)
+{
+  // Ensure mRuleList is constructed.
+  GetCssRulesInternal();
+  if (aIndex >= mRuleList->Length()) {
+    aRv.Throw(NS_ERROR_DOM_INDEX_SIZE_ERR);
+    return;
+  }
+
+  mozAutoDocUpdate updateBatch(mDocument, UPDATE_STYLE, true);
+  // Hold a strong ref to the rule so it doesn't die when we remove it
+  // from the list. XXX We may not want to hold it if stylesheet change
+  // event is not enabled.
+  RefPtr<css::Rule> rule = mRuleList->GetRule(aIndex);
+  aRv = mRuleList->DeleteRule(aIndex);
+  MOZ_ASSERT(!aRv.ErrorCodeIs(NS_ERROR_DOM_INDEX_SIZE_ERR),
+             "IndexSizeError should have been handled earlier");
+  if (!aRv.Failed()) {
+    RuleRemoved(*rule);
+  }
+}
+
+nsresult
+StyleSheet::InsertRuleIntoGroupInternal(const nsAString& aRule,
+                                             css::GroupRule* aGroup,
+                                             uint32_t aIndex)
+{
+  auto rules = static_cast<ServoCSSRuleList*>(aGroup->CssRules());
+  MOZ_ASSERT(rules->GetParentRule() == aGroup);
+  return rules->InsertRule(aRule, aIndex);
+}
+
+OriginFlags
+StyleSheet::GetOrigin()
+{
+  return static_cast<OriginFlags>(
+    Servo_StyleSheet_GetOrigin(Inner()->mContents));
+}
+
 } // namespace mozilla