Implement the gamepad API in the IPC proxy

ppapi/host/resource_host.h

 // Copyright (c) 2012 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.
 
 #ifndef PPAPI_HOST_RESOURCE_HOST_H_
 #define PPAPI_HOST_RESOURCE_HOST_H_
 
 #include "base/basictypes.h"
 #include "ppapi/c/pp_resource.h"
 #include "ppapi/host/ppapi_host_export.h"
@@ skipping 21 matching lines @@
   PP_Instance pp_instance() const { return pp_instance_; }
   PP_Resource pp_resource() const { return pp_resource_; }
 
   // Handles messages associated with a given resource object. If the flags
   // indicate that a response is required, the return value of this function
   // will be sent as a resource message "response" along with the message
   // specified in the reply of the context.
   //
   // You can do a response asynchronously by returning PP_OK_COMPLETIONPENDING.
   // This will cause the reply to be skipped, and the class implementing this
-  // function will take responsibility for issuing the callback later.
+  // function will take responsibility for issuing the callback. The callback
+  // can be issued inside OnResourceMessageReceived before it returns, or at
+  // a future time.
   //
   // If you don't have a particular reply message, you can just ignore
   // the reply in the message context. However, if you have a reply more than
   // just the int32_t result code, set the reply to be the message of your
   // choosing.
   //
   // The default implementation just returns PP_ERROR_NOTSUPPORTED.
   virtual int32_t OnResourceMessageReceived(const IPC::Message& msg,
                                             HostMessageContext* context);
 
  private:
   // The host that owns this object.
   PpapiHost* host_;
 
   PP_Instance pp_instance_;
   PP_Resource pp_resource_;
 
   DISALLOW_COPY_AND_ASSIGN(ResourceHost);
 };
 
 }  // namespace host
 }  // namespace ppapi
 
 #endif  // PPAPI_HOST_RESOURCE_HOST_H_