Implement native bindings for cast extensions API

chrome/test/data/extensions/api_test/webrtc_cast/basics.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.
 
 chrome.test.runTests([
   function udpTransport() {
     chrome.webrtc.castUdpTransport.create(function(info) {
-      chrome.webrtc.start(info.transportId,
-                          {address: "127.0.0.1", port: 60613});
-      chrome.webrtc.stop(info.transportId);
-      chrome.webrtc.destroy(info.transportId);
+      chrome.webrtc.castUdpTransport.start(
+          info.transportId,
+          {address: "127.0.0.1", port: 60613});
+      chrome.webrtc.castUdpTransport.stop(info.transportId);
+      chrome.webrtc.castUdpTransport.destroy(info.transportId);
       chrome.test.succeed();
     });
-    // TODO(hclam): Remove this line when the API is actually working.
-    // This is there so the test can finish.
-    chrome.test.succeed();
   }
 ]);