Add a histogram for tracking web store promo

chrome/browser/dom_ui/app_launcher_handler.h

 // Copyright (c) 2010 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_APP_LAUNCHER_HANDLER_H_
 #define CHROME_BROWSER_DOM_UI_APP_LAUNCHER_HANDLER_H_
 #pragma once
 
 #include "base/scoped_ptr.h"
 #include "chrome/browser/dom_ui/dom_ui.h"
@@ skipping 76 matching lines @@
   // Monitor extension preference changes so that the DOM UI can be notified.
   PrefChangeRegistrar pref_change_registrar_;
 
   // Used to show confirmation UI for uninstalling/enabling extensions in
   // incognito mode.
   scoped_ptr<ExtensionInstallUI> install_ui_;
 
   // The id of the extension we are prompting the user about.
   std::string extension_id_prompting_;
 
+  // Whether the promo is currently being shown
+  bool promo_active_;
+
   DISALLOW_COPY_AND_ASSIGN(AppLauncherHandler);
 };
 
 #endif  // CHROME_BROWSER_DOM_UI_APP_LAUNCHER_HANDLER_H_