Change to pass by const reference for a couple GCMDriverDesktop methods

components/gcm_driver/gcm_driver_desktop.cc

 // Copyright 2014 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.
 
 #include "components/gcm_driver/gcm_driver_desktop.h"
 
 #include <algorithm>
 #include <utility>
 
 #include "base/bind.h"
@@ skipping 728 matching lines @@
   if (callback_iter == send_callbacks_.end()) {
     // The callback could have been removed when the app is uninstalled.
     return;
   }
 
   SendCallback callback = callback_iter->second;
   send_callbacks_.erase(callback_iter);
   callback.Run(message_id, result);
 }
 
-void GCMDriverDesktop::MessageReceived(const std::string& app_id,
-                                       GCMClient::IncomingMessage message) {
+void GCMDriverDesktop::MessageReceived(
+    const std::string& app_id,
+    const GCMClient::IncomingMessage& message) {
   DCHECK(ui_thread_->RunsTasksOnCurrentThread());
 
   // Drop the event if signed out.
   if (account_id_.empty())
     return;
 
   GetAppHandler(app_id)->OnMessage(app_id, message);
 }
 
 void GCMDriverDesktop::MessagesDeleted(const std::string& app_id) {
@@ skipping 22 matching lines @@
   DCHECK(ui_thread_->RunsTasksOnCurrentThread());
 
   if (gcm_client_ready_)
     return;
   gcm_client_ready_ = true;
 
   delayed_task_controller_->SetReady();
 }
 
 void GCMDriverDesktop::GetGCMStatisticsFinished(
-    GCMClient::GCMStatistics stats) {
+    const GCMClient::GCMStatistics& stats) {
   DCHECK(ui_thread_->RunsTasksOnCurrentThread());
 
   // Normally request_gcm_statistics_callback_ would not be null.
   if (!request_gcm_statistics_callback_.is_null())
     request_gcm_statistics_callback_.Run(stats);
   else
     LOG(WARNING) << "request_gcm_statistics_callback_ is NULL.";
 }
 
 std::string GCMDriverDesktop::SignedInUserName() const {
   if (IsStarted())
     return identity_provider_->GetActiveUsername();
   return std::string();
 }
 
 }  // namespace gcm