Fix running default browser check/setting in UI thread on Linux....

chrome/browser/gtk/options/general_page_gtk.h

 // Copyright (c) 2006-2009 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_GTK_OPTIONS_GENERAL_PAGE_GTK_H_
 #define CHROME_BROWSER_GTK_OPTIONS_GENERAL_PAGE_GTK_H_
 
 #include <gtk/gtk.h>
 
 #include <string>
 #include <vector>
 
 #include "chrome/browser/cancelable_request.h"
 #include "chrome/browser/options_page_base.h"
 #include "chrome/browser/search_engines/template_url_model.h"
+#include "chrome/browser/shell_integration.h"
 #include "chrome/common/pref_member.h"
 #include "googleurl/src/gurl.h"
 
 class Profile;
 class ListStoreFavIconLoader;
 
 class GeneralPageGtk : public OptionsPageBase,
-                       public TemplateURLModelObserver {
+                       public TemplateURLModelObserver,
+                       public ShellIntegration::DefaultBrowserObserver {
  public:
   explicit GeneralPageGtk(Profile* profile);
   ~GeneralPageGtk();
 
   GtkWidget* get_page_widget() const {
     return page_;
   }
 
  private:
   // Overridden from OptionsPageBase
@@ skipping 85 matching lines @@
                                                   GeneralPageGtk* general_page);
 
   // Callback for use as default browser button
   static void OnBrowserUseAsDefaultClicked(GtkButton* button,
                                            GeneralPageGtk* general_page);
 
   // Enables/Disables the controls associated with the custom start pages
   // option if that preference is not selected.
   void EnableCustomHomepagesControls(bool enable);
 
-  // Sets the UI state to match
-  void SetDefaultBrowserUIState(bool is_default);
+  // ShellIntegration::DefaultBrowserObserver implementation.
+  virtual void SetDefaultBrowserUIState(
+      ShellIntegration::DefaultBrowserUIState state);
 
   // Widgets of the startup group
   GtkWidget* startup_homepage_radio_;
   GtkWidget* startup_last_session_radio_;
   GtkWidget* startup_custom_radio_;
   GtkWidget* startup_custom_pages_tree_;
   GtkListStore* startup_custom_pages_model_;
   GtkTreeSelection* startup_custom_pages_selection_;
   GtkWidget* startup_add_custom_page_button_;
   GtkWidget* startup_remove_custom_page_button_;
@@ skipping 27 matching lines @@
   // Flag to ignore gtk callbacks while we are loading prefs, to avoid
   // then turning around and saving them again.
   bool initializing_;
 
   // Used in loading favicons.
   CancelableRequestConsumer fav_icon_consumer_;
 
   // Helper to load the favicon pixbufs into the |startup_custom_pages_model_|.
   scoped_ptr<ListStoreFavIconLoader> favicon_loader_;
 
+  // The helper object that performs default browser set/check tasks.
+  scoped_refptr<ShellIntegration::DefaultBrowserWorker> default_browser_worker_;
+
   DISALLOW_COPY_AND_ASSIGN(GeneralPageGtk);
 };
 
 #endif  // CHROME_BROWSER_GTK_OPTIONS_GENERAL_PAGE_GTK_H_