Defer starting of animations until after compositing update

Source/core/core.gypi

 {
     'variables': {
         # Files for which bindings (.cpp and .h files) will be generated
         'core_idl_files': [
             'animation/Animation.idl',
             'animation/Player.idl',
             'animation/TimedItem.idl',
             'animation/Timeline.idl',
             'animation/Timing.idl',
             'clipboard/Clipboard.idl',
@@ skipping 557 matching lines @@
             'animation/AnimatableStrokeDasharrayList.h',
             'animation/AnimatableTransform.cpp',
             'animation/AnimatableTransform.h',
             'animation/AnimatableUnknown.h',
             'animation/AnimatableValue.cpp',
             'animation/AnimatableValue.h',
             'animation/AnimatableVisibility.cpp',
             'animation/AnimatableVisibility.h',
             'animation/Animation.cpp',
             'animation/Animation.h',
+            'animation/AnimationClock.cpp',
             'animation/AnimationClock.h',
             'animation/AnimationEffect.h',
             'animation/AnimationHelpers.h',
             'animation/AnimationStack.cpp',
             'animation/AnimationStack.h',
             'animation/AnimationTranslationUtil.cpp',
             'animation/AnimationTranslationUtil.h',
             'animation/CompositorAnimations.cpp',
             'animation/CompositorAnimations.h',
             'animation/CompositorAnimationsImpl.h',
@@ skipping 2689 matching lines @@
             'html/parser/HTMLParserThreadTest.cpp',
             'html/track/vtt/BufferedLineReaderTest.cpp',
             'html/track/vtt/VTTScannerTest.cpp',
             'rendering/RenderOverflowTest.cpp',
             'rendering/shapes/BoxShapeTest.cpp',
             'testing/UnitTestHelpers.cpp',
             'testing/UnitTestHelpers.h',
         ],
     }
 }