Bug 1073336 part 8 - Add protected AnimationPlayer::GetRenderedDocument(); r=dbaron

In order for AnimationPlayer objects to be able to notify their
collection/manager, the can either store an extra pointer member, or they can
navigate to the collection as follows:

  player->source(animation)->target(element)->document
    ->presShell->presContext->manager->collection

This patch adds a getter for the first part of this journey up to the document.

dom/animation/AnimationPlayer.cpp

@@ -6,6 +6,7 @@
 #include "AnimationPlayer.h"
 #include "AnimationUtils.h"
 #include "mozilla/dom/AnimationPlayerBinding.h"
+#include "nsIDocument.h" // For nsIDocument
 #include "nsLayoutUtils.h" // For PostRestyleEvent (remove after bug 1073336)
 
 namespace mozilla {
@@ -205,18 +206,7 @@ AnimationPlayer::ComposeStyle(nsRefPtr<css::AnimValuesStyleRule>& aStyleRule,
 void
 AnimationPlayer::FlushStyle() const
 {
-  if (!mSource) {
-    return;
-  }
-
-  Element* targetElement;
-  nsCSSPseudoElements::Type pseudoType;
-  mSource->GetTarget(targetElement, pseudoType);
-  if (!targetElement) {
-    return;
-  }
-
-  nsIDocument* doc = targetElement->GetComposedDoc();
+  nsIDocument* doc = GetRenderedDocument();
   if (doc) {
     doc->FlushPendingNotifications(Flush_Style);
   }
@@ -254,5 +244,22 @@ AnimationPlayer::SourceContentEnd() const
          + mSource->GetComputedTiming().mActiveDuration;
 }
 
+nsIDocument*
+AnimationPlayer::GetRenderedDocument() const
+{
+  if (!mSource) {
+    return nullptr;
+  }
+
+  Element* targetElement;
+  nsCSSPseudoElements::Type pseudoType;
+  mSource->GetTarget(targetElement, pseudoType);
+  if (!targetElement) {
+    return nullptr;
+  }
+
+  return targetElement->GetComposedDoc();
+}
+
 } // namespace dom
 } // namespace mozilla

dom/animation/AnimationPlayer.h

@@ -22,6 +22,7 @@
 
 struct JSContext;
 class nsCSSPropertySet;
+class nsIDocument;
 
 namespace mozilla {
 namespace css {
@@ -126,6 +127,8 @@ protected:
   void MaybePostRestyle() const;
   StickyTimeDuration SourceContentEnd() const;
 
+  nsIDocument* GetRenderedDocument() const;
+
   nsRefPtr<AnimationTimeline> mTimeline;
   nsRefPtr<Animation> mSource;
   Nullable<TimeDuration> mHoldTime;  // Player timescale