Remove content::NotificationObserver dependency from most Prefs code.

chrome/browser/ui/gtk/bookmarks/bookmark_bar_gtk.h

Index: chrome/browser/ui/gtk/bookmarks/bookmark_bar_gtk.h
diff --git a/chrome/browser/ui/gtk/bookmarks/bookmark_bar_gtk.h b/chrome/browser/ui/gtk/bookmarks/bookmark_bar_gtk.h
index 774c07666a8cb99f6540d7d6accfaf241037ca5d..61f78a6b2ec6fc474164d9491a9cc18f29854cd5 100644
--- a/chrome/browser/ui/gtk/bookmarks/bookmark_bar_gtk.h
+++ b/chrome/browser/ui/gtk/bookmarks/bookmark_bar_gtk.h
@@ -13,6 +13,7 @@
 #include "base/gtest_prod_util.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
+#include "base/prefs/public/pref_observer.h"
 #include "chrome/browser/api/prefs/pref_member.h"
 #include "chrome/browser/bookmarks/bookmark_model_observer.h"
 #include "chrome/browser/ui/bookmarks/bookmark_bar.h"
@@ -46,6 +47,7 @@ class BookmarkBarGtk : public ui::AnimationDelegate,
                        public BookmarkModelObserver,
                        public MenuBarHelper::Delegate,
                        public content::NotificationObserver,
+                       public PrefObserver,
                        public chrome::BookmarkBarInstructionsDelegate,
                        public BookmarkContextMenuControllerDelegate {
  public:
@@ -236,6 +238,11 @@ class BookmarkBarGtk : public ui::AnimationDelegate,
                        const content::NotificationSource& source,
                        const content::NotificationDetails& details) OVERRIDE;
 
+  // Overridden from PrefObserver:
+  virtual void OnPreferenceChanged(PrefServiceBase* service,
+                                   const std::string& pref_name) OVERRIDE;
+
+
   GtkWidget* CreateBookmarkButton(const BookmarkNode* node);
   GtkToolItem* CreateBookmarkToolItem(const BookmarkNode* node);