Add decrypt-only external clear key browser tests.

chrome/test/data/media/encrypted_media_utils.js

 // Copyright 2013 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.
 
 var keySystem = QueryString.keysystem;
 var mediaFile = QueryString.mediafile;
 var mediaType = QueryString.mediatype || 'video/webm; codecs="vorbis, vp8"';
 var useMSE = QueryString.usemse == 1;
 
 // Default key used to encrypt many media files used in browser tests.
@@ skipping 86 matching lines @@
 
     // keymessage in response to generateKeyRequest. Reply with key.
     console.log('onKeyMessage - key request', e);
     var initData = e.message;
     if (mediaType.indexOf('mp4') != -1)
       initData = KEY_ID; // Temporary hack for Clear Key in v0.1.
     video.webkitAddKey(keySystem, key, initData);
   }
 
   function verifyHeartbeatMessage(e) {
+    String.prototype.startsWith = function(prefix) {
+      return this.indexOf(prefix) === 0;
+    }
+
+    function isExternalClearKey(keySystem) {
+      return keySystem == EXTERNAL_CLEAR_KEY_KEY_SYSTEM ||
+             keySystem.startsWith(EXTERNAL_CLEAR_KEY_KEY_SYSTEM + '.');
+    }
+
     // Only External Clear Key sends a HEARTBEAT message.
-    if (e.keySystem != EXTERNAL_CLEAR_KEY_KEY_SYSTEM) {
+    if (!isExternalClearKey(e.keySystem)) {
       failTest('Unexpected heartbeat from ' + e.keySystem);
       return;
     }
 
     if (e.defaultURL != EXTERNAL_CLEAR_KEY_HEARTBEAT_URL) {
       failTest('Heartbeat message with unexpected defaultURL: ' + e.defaultURL);
       return;
     }
   }
 
@@ skipping 14 matching lines @@
   }
 }
 
 function getInitDataFromKeyId(keyID) {
   var init_key_id = new Uint8Array(keyID.length);
   for(var i = 0; i < keyID.length; i++) {
     init_key_id[i] = keyID.charCodeAt(i);
   }
   return init_key_id;
 }