Add srcObject attribute of type MediaStream to HTMLMediaElement.

third_party/WebKit/Source/modules/srcobject/HTMLMediaElementSrcObject.idl

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// https://html.spec.whatwg.org/multipage/embedded-content.html#dom-media-srcobject
+
+// TODO(guidou): Add support for MediaSource and Blob, as defined in the spec.
+typedef MediaStream MediaProvider;
+
+[
+    RuntimeEnabled=SrcObject
+] partial interface HTMLMediaElement {
+    // TODO(haraken): Per the spec, the srcObject should be defined in
+    // HTMLMediaElement.idl. However, we cannot define srcObject in 
+    // HTMLMediaElement.idl because of the dependency restriction from modules/
+    // to core/. For now we avoid the problem by using a partial interface.
+    attribute MediaProvider? srcObject;
+};