--- a/dom/base/nsDOMWindowUtils.cpp
+++ b/dom/base/nsDOMWindowUtils.cpp
@@ -11,16 +11,17 @@
 #include "nsPresContext.h"
 #include "nsError.h"
 #include "nsQueryContentEventResult.h"
 #include "nsGlobalWindow.h"
 #include "nsIDocument.h"
 #include "nsFocusManager.h"
 #include "nsFrameManager.h"
 #include "nsRefreshDriver.h"
+#include "mozilla/dom/Animation.h"
 #include "mozilla/dom/BindingDeclarations.h"
 #include "mozilla/dom/BlobBinding.h"
 #include "mozilla/dom/Event.h"
 #include "mozilla/dom/Touch.h"
 #include "mozilla/PendingAnimationTracker.h"
 #include "nsIObjectLoadingContent.h"
 #include "nsFrame.h"
 #include "mozilla/layers/ShadowLayers.h"
@@ -3801,16 +3802,43 @@ nsDOMWindowUtils::GetOMTCTransform(Eleme
 
   nsAutoString text;
   ErrorResult rv;
   cssValue->GetCssText(text, rv);
   aResult.Assign(text);
   return rv.StealNSResult();
 }
 
+NS_IMETHODIMP
+nsDOMWindowUtils::IsAnimationInPendingTracker(dom::Animation* aAnimation,
+                                              bool* aRetVal)
+{
+  MOZ_ASSERT(aRetVal);
+
+  if (!aAnimation) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  nsIDocument* doc = GetDocument();
+  if (!doc) {
+    *aRetVal = false;
+    return NS_OK;
+  }
+
+  PendingAnimationTracker* tracker = doc->GetPendingAnimationTracker();
+  if (!tracker) {
+    *aRetVal = false;
+    return NS_OK;
+  }
+
+  *aRetVal = tracker->IsWaitingToPlay(*aAnimation) ||
+             tracker->IsWaitingToPause(*aAnimation);
+  return NS_OK;
+}
+
 namespace {
 
 class HandlingUserInputHelper final : public nsIJSRAIIHelper
 {
 public:
   explicit HandlingUserInputHelper(bool aHandlingUserInput);
 
   NS_DECL_ISUPPORTS

--- a/dom/interfaces/base/nsIDOMWindowUtils.idl
+++ b/dom/interfaces/base/nsIDOMWindowUtils.idl
@@ -39,16 +39,17 @@ interface nsIFile;
 interface nsIURI;
 interface nsIRunnable;
 interface nsITranslationNodeList;
 interface nsIJSRAIIHelper;
 interface nsIContentPermissionRequest;
 interface nsIObserver;
 interface nsIDOMStorage;
 
+webidl Animation;
 webidl DOMRect;
 webidl Element;
 webidl EventTarget;
 webidl Event;
 webidl Node;
 webidl NodeList;
 
 [scriptable, uuid(4d6732ca-9da7-4176-b8a1-8dde15cd0bf9)]
@@ -1702,16 +1703,22 @@ interface nsIDOMWindowUtils : nsISupport
    * Unlike the above getOMTAStyle, the transform value returned by this
    * includes both of animating and APZ values.
    * Note: This function doesn't work on WebRender at all.  Also this function
    * does work only for transform layer and opacity layer with animations.
    */
   AString getOMTCTransform(in Element aElement,
                            [optional] in AString aPseudoElement);
 
+  /*
+   * Returns true if the given animation is being tracked by the pending
+   * animation tracker for the current document.
+   */
+  bool isAnimationInPendingTracker(in Animation aAnimation);
+
   /**
    * If aHandlingInput is true, this informs the event state manager that
    * we're handling user input. Otherwise, this is a no-op (as by default
    * we're not handling user input).
    * Remember to call destruct() on the return value!
    * See also nsIDOMWindowUtils::isHandlingUserInput.
    */
   nsIJSRAIIHelper setHandlingUserInput(in boolean aHandlingInput);