[Media Router] Do not issue a tab mirroring sinks query if tab is not valid.

chrome/browser/ui/webui/media_router/media_router_ui.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_ui.h"
 
 #include <algorithm>
 #include <string>
 #include <utility>
 
@@ skipping 246 matching lines @@
   collator_.reset(
       icu::Collator::createInstance(icu::Locale(locale.c_str()), error));
   if (U_FAILURE(error)) {
     DLOG(ERROR) << "Failed to create collator for locale " << locale;
     collator_.reset();
   }
 
   query_result_manager_.reset(new QueryResultManager(router_));
   query_result_manager_->AddObserver(this);
 
-  // These modes are always available.
+  // Desktop mirror mode is always available.
   query_result_manager_->StartSinksQuery(MediaCastMode::DESKTOP_MIRROR,
                                          MediaSourceForDesktop());
   initiator_ = initiator;
-  MediaSource mirroring_source(
-      MediaSourceForTab(SessionTabHelper::IdForTab(initiator)));
-  query_result_manager_->StartSinksQuery(MediaCastMode::TAB_MIRROR,
-                                         mirroring_source);
+  SessionID::id_type tab_id = SessionTabHelper::IdForTab(initiator);
+  if (tab_id != -1) {
+    MediaSource mirroring_source(MediaSourceForTab(tab_id));
+    query_result_manager_->StartSinksQuery(MediaCastMode::TAB_MIRROR,
+                                           mirroring_source);
+  }
   UpdateCastModes();
 }
 
 void MediaRouterUI::InitForTest(MediaRouter* router,
                                 content::WebContents* initiator,
                                 MediaRouterWebUIMessageHandler* handler) {
   router_ = router;
   handler_ = handler;
   InitCommon(initiator);
 }
@@ skipping 287 matching lines @@
         base::Time::Now() - start_time_);
     start_time_ = base::Time();
   }
 }
 
 void MediaRouterUI::UpdateMaxDialogHeight(int height) {
   handler_->UpdateMaxDialogHeight(height);
 }
 
 }  // namespace media_router