Web Animations: Add a runtime flag for playback control

This will guard the next shipping subset of the Web Animations API.

BUG=396369

Review URL: https://codereview.chromium.org/538503002

git-svn-id: svn://svn.chromium.org/blink/trunk@181696 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/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;

third_party/WebKit/Source/platform/RuntimeEnabledFeatures.in

@@ -144,6 +144,7 @@ TouchIconLoading
 ThreadedParserDataReceiver status=experimental
 UserSelectAll status=experimental
 WebAnimationsAPI status=experimental
+WebAnimationsPlaybackControl status=experimental
 WebAudio condition=WEB_AUDIO, status=stable
 WebGLDraftExtensions status=experimental
 WebGLImageChromium