[Media Router] Only keep track of toolbar MediaRouterAction in MediaRouterDialogControllerImpl.

chrome/browser/ui/webui/media_router/media_router_dialog_controller_impl.cc

 // Copyright 2015 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 "chrome/browser/ui/webui/media_router/media_router_dialog_controller_impl.h"
 
 #include <string>
 #include <vector>
 
 #include "base/trace_event/trace_event.h"
@@ skipping 154 matching lines @@
 MediaRouterDialogControllerImpl::~MediaRouterDialogControllerImpl() {
 }
 
 WebContents* MediaRouterDialogControllerImpl::GetMediaRouterDialog() const {
   DCHECK(thread_checker_.CalledOnValidThread());
   return dialog_observer_.get() ? dialog_observer_->web_contents() : nullptr;
 }
 
 void MediaRouterDialogControllerImpl::SetMediaRouterAction(
     const base::WeakPtr<MediaRouterAction>& action) {
-  action_ = action;
+  if (!action_)
+    action_ = action;
 }
 
 bool MediaRouterDialogControllerImpl::IsShowingMediaRouterDialog() const {
   return GetMediaRouterDialog() != nullptr;
 }
 
 void MediaRouterDialogControllerImpl::CloseMediaRouterDialog() {
   WebContents* media_router_dialog = GetMediaRouterDialog();
   if (!media_router_dialog)
     return;
@@ skipping 105 matching lines @@
           ->GetWeakPtr();
   if (!create_connection_request.get()) {
     media_router_ui->InitWithDefaultMediaSource(delegate);
   } else {
     media_router_ui->InitWithPresentationSessionRequest(
         initiator(), delegate, create_connection_request.Pass());
   }
 }
 
 }  // namespace media_router