Defer starting of animations until after compositing update

Source/core/animation/DocumentAnimations.cpp

Index: Source/core/animation/DocumentAnimations.cpp
diff --git a/Source/core/animation/DocumentAnimations.cpp b/Source/core/animation/DocumentAnimations.cpp
index 8bf72d2b7c61304bc17f3c35d19386e9fbcda9c5..38f402f53afe0db49b02285079bb330ff568ec62 100644
--- a/Source/core/animation/DocumentAnimations.cpp
+++ b/Source/core/animation/DocumentAnimations.cpp
@@ -50,8 +50,6 @@ void updateAnimationTiming(Document& document)
 {
     document.timeline()->serviceAnimations();
     document.transitionTimeline()->serviceAnimations();
-    if (!document.childNeedsStyleRecalc())
-        document.animationClock().unfreeze();
 }
 
 void dispatchAnimationEvents(Document& document)
@@ -68,8 +66,10 @@ void dispatchAnimationEventsAsync(Document& document)
 
 } // namespace
 
-void DocumentAnimations::serviceOnAnimationFrame(Document& document, double monotonicAnimationStartTime)
+void DocumentAnimations::serviceOnFrameStart(Document& document, double monotonicAnimationStartTime)
 {
+    // FIXME: This seems fragile. Do we need a separate frame lifecycle?
+    ASSERT(document.lifecycle().state() == DocumentLifecycle::StyleClean || document.lifecycle().state() == DocumentLifecycle::StyleRecalcPending || document.lifecycle().state() == DocumentLifecycle::LayoutClean || document.lifecycle().state() == DocumentLifecycle::CompositingClean);

[abarth-chromium, 2014/02/20 17:52:00]

What are you trying to assert here?  As written, this line of code doesn't make
sense.  If you write out what you're trying to assert in an english sentence, we
can figure out how to translate that into code.

[dstockwell, 2014/02/20 18:22:01]

I was looking at what we know about the beginning of a frame. When cc calls
animate we can be in any of these states.

Between the calls to animate and layout the DocumentLifecycle can traverse the
style/layout related states several times. We don't have a good way of knowing
where we are in the process of making a single frame.

     document.animationClock().updateTime(monotonicAnimationStartTime);
     updateAnimationTiming(document);
     dispatchAnimationEvents(document);
@@ -90,8 +90,9 @@ void DocumentAnimations::serviceBeforeGetComputedStyle(Node& node, CSSPropertyID
     }
 }
 
-void DocumentAnimations::serviceAfterStyleRecalc(Document& document)
+void DocumentAnimations::serviceOnFrameEnd(Document& document)
 {
+    ASSERT(document.lifecycle().state() == DocumentLifecycle::CompositingClean);
     if (document.cssPendingAnimations().startPendingAnimations() && document.view())
         document.view()->scheduleAnimation();