Schedule bitmap animation timers on the compositor task runner.

third_party/WebKit/Source/core/dom/TaskRunnerHelper.h

Index: third_party/WebKit/Source/core/dom/TaskRunnerHelper.h
diff --git a/third_party/WebKit/Source/core/dom/TaskRunnerHelper.h b/third_party/WebKit/Source/core/dom/TaskRunnerHelper.h
index 9389cdbcee5dd86f8dc2d2a10287962537eae4cd..1983cd78acea7c1324182f6f0221d060459b6c78 100644
--- a/third_party/WebKit/Source/core/dom/TaskRunnerHelper.h
+++ b/third_party/WebKit/Source/core/dom/TaskRunnerHelper.h
@@ -123,6 +123,9 @@ enum class TaskType : unsigned {
   // Tasks that must not be throttled should be posted here, but the usage
   // should be very limited.
   kUnthrottled,
+
+  // Tasks related to animating images should be posted here.

[Sami, 2017/04/27 17:38:17]

nit: No need to limit this to image animations -- could just say animations in
general.

[Dan Elphick, 2017/05/03 09:41:06]

no longer required

+  kAnimationTimer,
 };
 
 // HashTraits for TaskType.