Extensions: Move cast_channel and hid APIs to extensions/.

extensions/common/api/cast_channel.idl

 // 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.
 
 // API for communicating with a Google Cast device over an authenticated
 // channel.
 namespace cast.channel {
 
   // The state of the channel.
   enum ReadyState {
@@ skipping 150 matching lines @@
   interface Events {
     // Fired when a message is received on an open channel.
     static void onMessage(ChannelInfo channel,
                           MessageInfo message);
 
     // Fired when an error occurs as a result of a channel method or a network
     // event.
     static void onError(ChannelInfo channel);
   };
 };