Have HTMLMediaElement::play() return a Promise.

third_party/WebKit/Source/core/html/HTMLMediaElement.idl

 /*
  * Copyright (C) 2007, 2010, 2011, 2012 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 53 matching lines @@
     readonly attribute unrestricted double duration;
     // FIXME: Date getStartDate(); crbug.com/312699
     readonly attribute boolean paused;
     attribute double defaultPlaybackRate;
     attribute double playbackRate;
     readonly attribute TimeRanges played;
     readonly attribute TimeRanges seekable;
     readonly attribute boolean ended;
     [Reflect] attribute boolean autoplay;
     [Reflect] attribute boolean loop;
-    void play();
+    [CallWith=ScriptState, ImplementedAs=playForBindings] Promise<void> play();
     void pause();
 
     // controls
     [Reflect] attribute boolean controls;
     [RaisesException=Setter] attribute double volume;
     attribute boolean muted;
     [Reflect=muted] attribute boolean defaultMuted;
 
     // tracks
     [SameObject, RuntimeEnabled=AudioVideoTracks] readonly attribute AudioTrackList audioTracks;
     [SameObject, RuntimeEnabled=AudioVideoTracks] readonly attribute VideoTrackList videoTracks;
     [SameObject] readonly attribute TextTrackList textTracks;
     [RaisesException] TextTrack addTextTrack(TextTrackKind kind, optional DOMString label = "", optional DOMString language = "");
 
     // Non-standard APIs
     // The number of bytes consumed by the media decoder.
     [MeasureAs=PrefixedAudioDecodedByteCount] readonly attribute unsigned long webkitAudioDecodedByteCount;
     [MeasureAs=PrefixedVideoDecodedByteCount] readonly attribute unsigned long webkitVideoDecodedByteCount;
 };