Refactor some ResourceMessageReply usages.

ppapi/host/host_message_context.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_HOST_MESSAGE_CONTEXT_H_
 #define PPAPI_HOST_HOST_MESSAGE_CONTEXT_H_
 
 #include "ipc/ipc_message.h"
 #include "ppapi/host/ppapi_host_export.h"
 #include "ppapi/proxy/resource_message_params.h"
 
 namespace ppapi {
 namespace host {
 
 // This context structure provides information about outgoing resource message
 // replies.
 struct PPAPI_HOST_EXPORT ReplyMessageContext {
   ReplyMessageContext();
   ReplyMessageContext(
       const ppapi::proxy::ResourceMessageReplyParams& cp,
       IPC::Message* sync_reply_msg,
       int routing_id);
   ~ReplyMessageContext();
 
+  // Returns a value indicating whether this context is valid or "null".
+  bool is_valid() const { return params.pp_resource() != 0; }
+
   // The "reply params" struct with the same resource and sequence number
   // as the original resource message call.
   ppapi::proxy::ResourceMessageReplyParams params;
 
   // If this context is generated from a sync message, this will be set to the
   // incoming sync message. Otherwise, it will be NULL. The plugin controls
   // whether or not the resource call is synchronous or asynchronous so a
   // ResoureHost cannot make any assumptions about whether or not this is NULL.
   IPC::Message* sync_reply_msg;
 
@@ skipping 36 matching lines @@
   // Routing ID to be used when sending a reply message. This is only useful
   // when the plugin is in-process. Otherwise, the value will be
   // MSG_ROUTING_NONE.
   int routing_id;
 };
 
 }  // namespace host
 }  // namespace ppapi
 
 #endif  // PPAPI_HOST_HOST_MESSAGE_CONTEXT_H_