Web Animations: Don't participate in grouping when start time is set

Source/core/animation/CompositorPendingAnimations.cpp

Index: Source/core/animation/CompositorPendingAnimations.cpp
diff --git a/Source/core/animation/CompositorPendingAnimations.cpp b/Source/core/animation/CompositorPendingAnimations.cpp
index 06c0fd0c8c23e5c481deb94c3979575afdd2a711..f199978c2492e24e2f8f6a97b11700080bdda39d 100644
--- a/Source/core/animation/CompositorPendingAnimations.cpp
+++ b/Source/core/animation/CompositorPendingAnimations.cpp
@@ -72,7 +72,8 @@ bool CompositorPendingAnimations::update(bool startOnCompositor)
 
     for (auto& animation : animations) {
         bool hadCompositorAnimation = animation->hasActiveAnimationsOnCompositor();
-        if (animation->preCommit(compositorGroup, startOnCompositor)) {
+        // Animations with a start time do not participate in compositor start-time grouping.
+        if (animation->preCommit(animation->hasStartTime() ? 0 : compositorGroup, startOnCompositor)) {

[ctserng, 2015/09/14 14:30:32]

Will we run the risk of hitting the assert here:

https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...

             if (animation->hasActiveAnimationsOnCompositor() && !hadCompositorAnimation) {
                 startedSynchronizedOnCompositor = true;
             }