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 "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.
   void RegisterMessages() override {}
 
+  // 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::WebUIController:

[dschuyler, 2016/03/10 21:49:49]

s/:/./

[Dan Beam, 2016/03/11 00:07:12]

following the code below, as per the style guide:

"""
Parting Words

Use common sense and BE CONSISTENT.

If you are editing code, take a few minutes to look at the code around you and
determine its style. If they use spaces around their if clauses, you should,
too. If their comments have little boxes of stars around them, make your
comments have little boxes of stars around them too.
"""

+  void RenderViewReused(content::RenderViewHost* render_view_host) override;
+
   // Overridden from 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::vector<SettingsPageUIHandler*> handlers_;
 
   base::Time load_start_time_;
 
   DISALLOW_COPY_AND_ASSIGN(MdSettingsUI);
 };
 
 }  // namespace settings
 
 #endif  // CHROME_BROWSER_UI_WEBUI_SETTINGS_MD_SETTINGS_UI_H_