Have HTMLMediaElement::play() return a Promise.

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

 /*
  *  Copyright (C) 2006, 2007 Apple Inc. All rights reserved.
  *
  *  This library is free software; you can redistribute it and/or
  *  modify it under the terms of the GNU Lesser General Public
  *  License as published by the Free Software Foundation; either
  *  version 2 of the License, or (at your option) any later version.
  *
  *  This library is distributed in the hope that it will be useful,
  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 66 matching lines @@
     PathExistsError,
 
     // SQL
     SQLDatabaseError, // Naming conflict with DatabaseError class.
 
     // Web Crypto
     OperationError,
 
     // Push API
     PermissionDeniedError,
+
+    NotAllowedError,
+
+    // Please add new enums at the end of this list to guarantee any ordering
+    // expectations.
 };
 
 enum V8ErrorType {
     V8GeneralError = 1000,
     V8TypeError,
     V8RangeError,
     V8SyntaxError,
     V8ReferenceError,
 };
 
 } // namespace blink
 
 #endif // ExceptionCode_h