Improve New Tab Page load performance

chrome/browser/dom_ui/dom_ui_theme_source.h

 // Copyright (c) 2009 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_DOM_UI_DOM_UI_THEME_SOURCE_H_
 #define CHROME_BROWSER_DOM_UI_DOM_UI_THEME_SOURCE_H_
 
 #include <string>
 
 #include "chrome/browser/dom_ui/chrome_url_data_manager.h"
 
 class Profile;
 
 // ThumbnailSource is the gateway between network-level chrome:
 // requests for thumbnails and the history backend that serves these.
 class DOMUIThemeSource : public ChromeURLDataManager::DataSource {
  public:
   explicit DOMUIThemeSource(Profile* profile);
 
   // Called when the network layer has requested a resource underneath
   // the path we registered.
   virtual void StartDataRequest(const std::string& path, int request_id);
   virtual std::string GetMimeType(const std::string& path) const;
 
   virtual void SendResponse(int request_id, RefCountedBytes* data);
 
+  virtual MessageLoop* MessageLoopForRequestPath(const std::string& path) const;
+
  private:
-  // Generate and send the CSS for the new tab.
-  void SendNewTabCSS(int request_id);
+  // Populate new_tab_css_ and new_incognito_tab_css.  These must be called
+  // from the UI thread because they involve profile and theme access.
+  //
+  // A new DOMUIThemeSource object is used for each new tab page instance
+  // and each reload of an existing new tab page, so there is no concern about
+  // cached data becoming stale.
+  void InitNewTabCSS();
+  void InitNewIncognitoTabCSS();
 
-  // Generate and send the CSS for the new incognito tab.
-  void SendNewIncognitoTabCSS(int request_id);
+  // Send the CSS for the new tab or the new incognito tab.
+  void SendNewTabCSS(int request_id, const std::string& css_string);
 
   // Fetch and send the theme bitmap.
   void SendThemeBitmap(int request_id, int resource_id);
 
   // Get the CSS string for the background position on the new tab page for the
   // states when the bar is attached or detached.
   std::string GetNewTabBackgroundCSS(bool bar_attached);
 
   // How the background image on the new tab page should be tiled (see tiling
   // masks in browser_theme_provider.h).
   std::string GetNewTabBackgroundTilingCSS();
 
+  // The content to be served by SendNewTabCSS, stored by InitNewTabCSS and
+  // InitNewIncognitoTabCSS.
+  std::string new_tab_css_;
+  std::string new_incognito_tab_css_;
+
   Profile* profile_;
   DISALLOW_COPY_AND_ASSIGN(DOMUIThemeSource);
 };
 
 #endif  // CHROME_BROWSER_DOM_UI_DOM_UI_THEME_SOURCE_H_