Web Animations: Use an IDL enum for AnimationPlayState

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 ccd618f92b247f043ae6cc8431ed508ec244e89f..fa467b6dfb2c3ed1edc5e14950d82052cebf396a 100644
--- a/Source/core/animation/AnimationPlayer.idl
+++ b/Source/core/animation/AnimationPlayer.idl
@@ -28,6 +28,8 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+enum AnimationPlayState { "idle", "pending", "running", "paused", "finished" };
+
 [
     NoInterfaceObject,
     WillBeGarbageCollected,
@@ -37,7 +39,7 @@
     [RuntimeEnabled=WebAnimationsPlaybackControl]          attribute double     startTime;
     [RuntimeEnabled=WebAnimationsPlaybackControl]          attribute double     currentTime;
     [RuntimeEnabled=WebAnimationsPlaybackControl]          attribute double     playbackRate;
-    [RuntimeEnabled=WebAnimationsPlaybackControl] readonly attribute DOMString  playState;
+    [RuntimeEnabled=WebAnimationsPlaybackControl] readonly attribute AnimationPlayState playState;
     [RuntimeEnabled=WebAnimationsPlaybackControl, RaisesException] void finish();
     [RuntimeEnabled=WebAnimationsPlaybackControl] void play();
     [RuntimeEnabled=WebAnimationsPlaybackControl] void pause();