Bug 1344619 - Part 2: Introduce EffectCompositor::PreTraverse(). r=birtles

MozReview-Commit-ID: 6ijDJttB9eo

--HG--
extra : rebase_source : 451601b1daf37e7b36d0b8ecda71c34388b78412

dom/animation/EffectCompositor.cpp

@@ -940,6 +940,40 @@ EffectCompositor::SetPerformanceWarning(
   }
 }
 
+void
+EffectCompositor::PreTraverse()
+{
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(mPresContext->RestyleManager()->IsServo());
+
+  for (auto& elementsToRestyle : mElementsToRestyle) {
+    for (auto iter = elementsToRestyle.Iter(); !iter.Done(); iter.Next()) {
+      bool postedRestyle = iter.Data();
+      // Ignore throttled restyle.
+      if (!postedRestyle) {
+        continue;
+      }
+
+      NonOwningAnimationTarget target = iter.Key();
+      EffectSet* effects =
+        EffectSet::GetEffectSet(target.mElement, target.mPseudoType);
+      if (!effects) {
+        // Drop the EffectSets that have been destroyed.
+        iter.Remove();
+        continue;
+      }
+
+      for (KeyframeEffectReadOnly* effect : *effects) {
+        effect->GetAnimation()->WillComposeStyle();
+      }
+
+      // Remove the element from the list of elements to restyle since we are
+      // about to restyle it.
+      iter.Remove();
+    }
+  }
+}
+
 // ---------------------------------------------------------
 //
 // Nested class: AnimationStyleRuleProcessor

dom/animation/EffectCompositor.h

@@ -233,6 +233,11 @@ public:
     nsCSSPropertyID aProperty,
     const AnimationPerformanceWarning& aWarning);
 
+  // Do a bunch of stuff that we should avoid doing during the parallel
+  // traversal (e.g. changing member variables) for all elements that we expect
+  // to restyle on the next traversal.
+  void PreTraverse();
+
 private:
   ~EffectCompositor() = default;