MD Settings: avoid double pref observation on Startup Pages

chrome/browser/ui/webui/settings/md_settings_ui.h

 // Copyright (c) 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.
 
 #ifndef CHROME_BROWSER_UI_WEBUI_SETTINGS_MD_SETTINGS_UI_H_
 #define CHROME_BROWSER_UI_WEBUI_SETTINGS_MD_SETTINGS_UI_H_
 
 #include <string>
-#include <vector>
+#include <unordered_set>
 
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/time/time.h"
 #include "base/values.h"
 #include "content/public/browser/web_contents_observer.h"
 #include "content/public/browser/web_ui_controller.h"
 #include "content/public/browser/web_ui_message_handler.h"
 
 namespace settings {
 
 // The base class handler of Javascript messages of settings pages.
 class SettingsPageUIHandler : public content::WebUIMessageHandler {
  public:
   SettingsPageUIHandler();
   ~SettingsPageUIHandler() override;
 
-  // WebUIMessageHandler implementation.
+  // WebUIMessageHandler:
   void RegisterMessages() override {}
 
+  // Called when a navigation re-uses a renderer process (i.e. reload).
+  // TODO(dbeam): move to WebUIMessageHandler?
+  virtual void RenderViewReused() {}
+
  protected:
   // Helper method for responding to JS requests initiated with
   // cr.sendWithPromise(), for the case where the returned promise should be
   // resolved (request succeeded).
   void ResolveJavascriptCallback(const base::Value& callback_id,
                                  const base::Value& response);
 
   // Helper method for responding to JS requests initiated with
   // cr.sendWithPromise(), for the case where the returned promise should be
   // rejected (request failed).
   void RejectJavascriptCallback(const base::Value& callback_id,
                                 const base::Value& response);
 
  private:
   DISALLOW_COPY_AND_ASSIGN(SettingsPageUIHandler);
 };
 
 // The WebUI handler for chrome://md-settings.
 class MdSettingsUI : public content::WebUIController,
                      public content::WebContentsObserver {
  public:
   explicit MdSettingsUI(content::WebUI* web_ui);
   ~MdSettingsUI() override;
 
-  // Overridden from content::WebContentsObserver:
+  // content::WebUIController:
+  void RenderViewReused(content::RenderViewHost* render_view_host) override;
+
+  // content::WebContentsObserver:
   void DidStartProvisionalLoadForFrame(
       content::RenderFrameHost* render_frame_host,
       const GURL& validated_url,
       bool is_error_page,
       bool is_iframe_srcdoc) override;
   void DocumentLoadedInFrame(
       content::RenderFrameHost *render_frame_host) override;
   void DocumentOnLoadCompletedInMainFrame() override;
 
  private:
-  void AddSettingsPageUIHandler(content::WebUIMessageHandler* handler);
+  void AddSettingsPageUIHandler(SettingsPageUIHandler* handler);
+
+  // Weak references; all |handlers_| are owned by |web_ui()|.
+  std::unordered_set<SettingsPageUIHandler*> handlers_;
 
   base::Time load_start_time_;
 
   DISALLOW_COPY_AND_ASSIGN(MdSettingsUI);
 };
 
 }  // namespace settings
 
 #endif  // CHROME_BROWSER_UI_WEBUI_SETTINGS_MD_SETTINGS_UI_H_