Remove content::NotificationObserver dependency from most Prefs code.

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

Index: chrome/browser/ui/gtk/bookmarks/bookmark_bar_gtk.cc
diff --git a/chrome/browser/ui/gtk/bookmarks/bookmark_bar_gtk.cc b/chrome/browser/ui/gtk/bookmarks/bookmark_bar_gtk.cc
index 3b1b9124637fb01e7e851887e181b2e0bd5af99b..7f1b30b3d90675aed902dfd704c7d4d7d7d5e913 100644
--- a/chrome/browser/ui/gtk/bookmarks/bookmark_bar_gtk.cc
+++ b/chrome/browser/ui/gtk/bookmarks/bookmark_bar_gtk.cc
@@ -980,14 +980,15 @@ void BookmarkBarGtk::Observe(int type,
     }
 
     SetOverflowButtonAppearance();
-  } else if (type == chrome::NOTIFICATION_PREF_CHANGED) {
-    const std::string& pref_name =
-        *content::Details<std::string>(details).ptr();
-    if (pref_name == prefs::kEditBookmarksEnabled)
-      OnEditBookmarksEnabledChanged();
   }
 }
 
+void BookmarkBarGtk::OnPreferenceChanged(PrefServiceBase* service,
+                                         const std::string& pref_name) {
+  if (pref_name == prefs::kEditBookmarksEnabled)
+    OnEditBookmarksEnabledChanged();
+}
+
 GtkWidget* BookmarkBarGtk::CreateBookmarkButton(const BookmarkNode* node) {
   GtkWidget* button = theme_service_->BuildChromeButton();
   bookmark_utils::ConfigureButtonForNode(node, model_, button, theme_service_);