--- a/layout/style/nsRuleNode.cpp
+++ b/layout/style/nsRuleNode.cpp
@@ -364,42 +364,57 @@ static inline nscoord ScaleViewportCoord
   // repeatedly use a value and expect some multiple of the value to be
   // smaller than a container, we need to use floor rather than round.
   // We need to use division by 100.0 rather than multiplication by 0.1f
   // to avoid introducing error.
   return NSToCoordTruncClamped(aValue.GetFloatValue() *
                                aViewportSize / 100.0f);
 }
 
+/* static */
 already_AddRefed<nsFontMetrics>
-GetMetricsFor(nsPresContext* aPresContext,
-              nsStyleContext* aStyleContext,
-              const nsStyleFont* aStyleFont,
-              nscoord aFontSize, // overrides value from aStyleFont
-              bool aUseUserFontSet)
+nsRuleNode::GetMetricsFor(nsPresContext* aPresContext,
+                          bool aIsVertical,
+                          const nsStyleFont* aStyleFont,
+                          nscoord aFontSize,
+                          bool aUseUserFontSet)
 {
   nsFont font = aStyleFont->mFont;
   font.size = aFontSize;
-  gfxFont::Orientation orientation = gfxFont::eHorizontal;
-  if (aStyleContext) {
-    WritingMode wm(aStyleContext);
-    if (wm.IsVertical() && !wm.IsSideways()) {
-      orientation = gfxFont::eVertical;
-    }
-  }
+  gfxFont::Orientation orientation
+    = aIsVertical ? gfxFont::eVertical : gfxFont::eHorizontal;
   nsFontMetrics::Params params;
   params.language = aStyleFont->mLanguage;
   params.explicitLanguage = aStyleFont->mExplicitLanguage;
   params.orientation = orientation;
   params.userFontSet =
     aUseUserFontSet ? aPresContext->GetUserFontSet() : nullptr;
   params.textPerf = aPresContext->GetTextPerfMetrics();
   return aPresContext->DeviceContext()->GetMetricsFor(font, params);
 }
 
+/* static */
+already_AddRefed<nsFontMetrics>
+nsRuleNode::GetMetricsFor(nsPresContext* aPresContext,
+                          nsStyleContext* aStyleContext,
+                          const nsStyleFont* aStyleFont,
+                          nscoord aFontSize, // overrides value from aStyleFont
+                          bool aUseUserFontSet)
+{
+  bool isVertical = false;
+  if (aStyleContext) {
+    WritingMode wm(aStyleContext);
+    if (wm.IsVertical() && !wm.IsSideways()) {
+      isVertical = true;
+    }
+  }
+  return nsRuleNode::GetMetricsFor(aPresContext, isVertical, aStyleFont,
+                                   aFontSize, aUseUserFontSet);
+}
+
 
 static nsSize CalcViewportUnitsScale(nsPresContext* aPresContext)
 {
   // The caller is making use of viewport units, so notify the pres context
   // that it will need to rebuild the rule tree if the size of the viewport
   // changes.
   aPresContext->SetUsesViewportUnits(true);
 

--- a/layout/style/nsRuleNode.h
+++ b/layout/style/nsRuleNode.h
@@ -17,16 +17,17 @@
 #include "mozilla/RangedArray.h"
 #include "mozilla/RuleNodeCacheConditions.h"
 #include "mozilla/SheetType.h"
 #include "nsPresContext.h"
 #include "nsStyleStruct.h"
 
 class nsCSSPropertyIDSet;
 class nsCSSValue;
+class nsFontMetrics;
 class nsIStyleRule;
 class nsStyleContext;
 class nsStyleCoord;
 struct nsCSSRect;
 struct nsCSSValueList;
 struct nsCSSValuePairList;
 struct nsRuleData;
 
@@ -792,16 +793,28 @@ private:
 public:
   // This is infallible; it will never return nullptr.
   static already_AddRefed<nsRuleNode> CreateRootNode(nsPresContext* aPresContext);
 
   static void EnsureBlockDisplay(mozilla::StyleDisplay& display,
                                  bool aConvertListItem = false);
   static void EnsureInlineDisplay(mozilla::StyleDisplay& display);
 
+  static already_AddRefed<nsFontMetrics> GetMetricsFor(nsPresContext* aPresContext,
+                                                       bool aIsVertical,
+                                                       const nsStyleFont* aStyleFont,
+                                                       nscoord aFontSize,
+                                                       bool aUseUserFontSet);
+
+  static already_AddRefed<nsFontMetrics> GetMetricsFor(nsPresContext* aPresContext,
+                                                       nsStyleContext* aStyleContext,
+                                                       const nsStyleFont* aStyleFont,
+                                                       nscoord aFontSize,
+                                                       bool aUseUserFontSet);
+
   // Transition never returns null; on out of memory it'll just return |this|.
   nsRuleNode* Transition(nsIStyleRule* aRule, mozilla::SheetType aLevel,
                          bool aIsImportantRule);
   nsRuleNode* GetParent() const { return mParent; }
   bool IsRoot() const { return mParent == nullptr; }
 
   // Return the root of the rule tree that this rule node is in.
   nsRuleNode* RuleTree();