Web Animations: Add a runtime flag for playback control

Source/core/animation/AnimationPlayer.idl

Index: Source/core/animation/AnimationPlayer.idl
diff --git a/Source/core/animation/AnimationPlayer.idl b/Source/core/animation/AnimationPlayer.idl
index 00ef93e5d4181758ac9bfee3434e60cbfd4f1d37..ccd618f92b247f043ae6cc8431ed508ec244e89f 100644
--- a/Source/core/animation/AnimationPlayer.idl
+++ b/Source/core/animation/AnimationPlayer.idl
@@ -33,15 +33,15 @@
     WillBeGarbageCollected,
     ActiveDOMObject,
 ] interface AnimationPlayer : EventTarget {
-    [RuntimeEnabled=WebAnimationsAPI]          attribute AnimationNode? source;
-    [RuntimeEnabled=WebAnimationsAPI]          attribute double     startTime;
-    [RuntimeEnabled=WebAnimationsAPI]          attribute double     currentTime;
-    [RuntimeEnabled=WebAnimationsAPI]          attribute double     playbackRate;
-    [RuntimeEnabled=WebAnimationsAPI] readonly attribute DOMString  playState;
-    [RuntimeEnabled=WebAnimationsAPI, RaisesException] void finish();
-    [RuntimeEnabled=WebAnimationsAPI] void play();
-    [RuntimeEnabled=WebAnimationsAPI] void pause();
-    [RuntimeEnabled=WebAnimationsAPI] void reverse();
+    [RuntimeEnabled=WebAnimationsAPI]                      attribute AnimationNode? source;
+    [RuntimeEnabled=WebAnimationsPlaybackControl]          attribute double     startTime;
+    [RuntimeEnabled=WebAnimationsPlaybackControl]          attribute double     currentTime;
+    [RuntimeEnabled=WebAnimationsPlaybackControl]          attribute double     playbackRate;
+    [RuntimeEnabled=WebAnimationsPlaybackControl] readonly attribute DOMString  playState;
+    [RuntimeEnabled=WebAnimationsPlaybackControl, RaisesException] void finish();
+    [RuntimeEnabled=WebAnimationsPlaybackControl] void play();
+    [RuntimeEnabled=WebAnimationsPlaybackControl] void pause();
+    [RuntimeEnabled=WebAnimationsPlaybackControl] void reverse();
 
     void cancel();
     [MeasureAs=AnimationPlayerFinishEvent] attribute EventHandler onfinish;