MD Settings: avoid double pref observation on Startup Pages

chrome/browser/ui/webui/settings/settings_startup_pages_handler.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/settings/settings_startup_pages_handler.h"
 
 #include <string>
 #include <vector>
 
 #include "chrome/browser/prefs/session_startup_pref.h"
@@ skipping 22 matching lines @@
       base::Bind(&StartupPagesHandler::OnStartupPrefsPageLoad,
                  base::Unretained(this)));
   web_ui()->RegisterMessageCallback("removeStartupPage",
       base::Bind(&StartupPagesHandler::RemoveStartupPage,
                  base::Unretained(this)));
   web_ui()->RegisterMessageCallback("setStartupPagesToCurrentPages",
       base::Bind(&StartupPagesHandler::SetStartupPagesToCurrentPages,
                  base::Unretained(this)));
 }
 
+void StartupPagesHandler::RenderViewReused() {
+  startup_custom_pages_table_model_.SetObserver(nullptr);
+  pref_change_registrar_.RemoveAll();
+}
+
 void StartupPagesHandler::OnModelChanged() {
   base::ListValue startup_pages;
   int page_count = startup_custom_pages_table_model_.RowCount();
   std::vector<GURL> urls = startup_custom_pages_table_model_.GetURLs();
   for (int i = 0; i < page_count; ++i) {
     scoped_ptr<base::DictionaryValue> entry(new base::DictionaryValue());
     entry->SetString("title", startup_custom_pages_table_model_.GetText(i, 0));
     entry->SetString("url", urls[i].spec());
     entry->SetString("tooltip",
                      startup_custom_pages_table_model_.GetTooltip(i));
@@ skipping 98 matching lines @@
 
 void StartupPagesHandler::UpdateStartupPages() {
   const SessionStartupPref startup_pref = SessionStartupPref::GetStartupPref(
       Profile::FromWebUI(web_ui())->GetPrefs());
   startup_custom_pages_table_model_.SetURLs(startup_pref.urls);
   // The change will go to the JS code in the
   // StartupPagesHandler::OnModelChanged() method.
 }
 
 }  // namespace settings