Have HTMLMediaElement::play() return a Promise.

third_party/WebKit/Source/core/dom/DOMException.cpp

Index: third_party/WebKit/Source/core/dom/DOMException.cpp
diff --git a/third_party/WebKit/Source/core/dom/DOMException.cpp b/third_party/WebKit/Source/core/dom/DOMException.cpp
index a8b1414ebac5629ed43768d09c9953887f6c5821..144aadf29bb6214b1376f1b4c79cec2af4f07db7 100644
--- a/third_party/WebKit/Source/core/dom/DOMException.cpp
+++ b/third_party/WebKit/Source/core/dom/DOMException.cpp
@@ -81,6 +81,11 @@ static const struct CoreException {
 
     // Push API
     { "PermissionDeniedError", "User or security policy denied the request.", 0 },
+
+    { "NotAllowedError", "The request is not allowed by the user agent or the platform in the current context.", 0 },
+
+    // Please add new entries at the end of this list to guarantee any ordering
+    // expectations.
 };
 
 static const CoreException* getErrorEntry(ExceptionCode ec)