Adds support for media permission request handling on <appview> tag.

extensions/test/data/app_view/apitest/media_request/main.js

+// Copyright 2014 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.
+
+window.onload = function() {
+  var webview = document.createElement("webview");
+  webview.partition = "media";
+  webview.addEventListener("permissionrequest", function(e) {
+    if (e.permission == "media") {
+      e.request.allow();
+    }
+  });
+  document.body.appendChild(webview);
+  webview.src = "guest.html";
+}