Web Animations CSS: Unfreeze AnimationClock if sampling timelines does not trigger style recalc

Source/core/frame/FrameView.cpp

Index: Source/core/frame/FrameView.cpp
diff --git a/Source/core/frame/FrameView.cpp b/Source/core/frame/FrameView.cpp
index 6616db7c3cd36690d4cb0f9e6a76580469031ad9..6b2557a41832e1f877a4a0e9719247854652ff0d 100644
--- a/Source/core/frame/FrameView.cpp
+++ b/Source/core/frame/FrameView.cpp
@@ -30,6 +30,7 @@
 #include "HTMLNames.h"
 #include "RuntimeEnabledFeatures.h"
 #include "core/accessibility/AXObjectCache.h"
+#include "core/animation/AnimationClock.h"
 #include "core/animation/DocumentTimeline.h"
 #include "core/css/FontFaceSet.h"
 #include "core/css/resolver/StyleResolver.h"
@@ -2025,8 +2026,11 @@ void FrameView::serviceScriptedAnimations(double monotonicAnimationStartTime)
         if (!RuntimeEnabledFeatures::webAnimationsCSSEnabled())
             frame->animation().serviceAnimations();
         if (RuntimeEnabledFeatures::webAnimationsEnabled()) {
-            frame->document()->timeline()->serviceAnimations(monotonicAnimationStartTime);
-            frame->document()->transitionTimeline()->serviceAnimations(monotonicAnimationStartTime);
+            frame->document()->animationClock().updateTime(monotonicAnimationStartTime);
+            bool didTriggerStyleRecalc = frame->document()->timeline()->serviceAnimations();

[dstockwell, 2013/11/05 05:05:44]

It's unfortunate that we have to thread this all the way out. Wouldn't it be
sufficient to test !(frame->document->needsStyleRecalc() ||
...->childNeedsStyleRecalc()) ?

+            didTriggerStyleRecalc |= frame->document()->transitionTimeline()->serviceAnimations();
+            if (!didTriggerStyleRecalc)
+                frame->document()->animationClock().unfreeze();
             frame->document()->timeline()->dispatchEvents();
             frame->document()->transitionTimeline()->dispatchEvents();
         }