Remove content::NotificationObserver dependency from most Prefs code.

chrome/browser/ui/cocoa/location_bar/location_bar_view_mac.mm

Index: chrome/browser/ui/cocoa/location_bar/location_bar_view_mac.mm
diff --git a/chrome/browser/ui/cocoa/location_bar/location_bar_view_mac.mm b/chrome/browser/ui/cocoa/location_bar/location_bar_view_mac.mm
index b560bcdfa0d7f2c752bad6aaa13835240d7c99c1..11489925cdc2398908e63448bbfe6e779ea1a370 100644
--- a/chrome/browser/ui/cocoa/location_bar/location_bar_view_mac.mm
+++ b/chrome/browser/ui/cocoa/location_bar/location_bar_view_mac.mm
@@ -593,17 +593,18 @@ void LocationBarViewMac::Observe(int type,
       break;
     }
 
-    case chrome::NOTIFICATION_PREF_CHANGED:
-      UpdateStarDecorationVisibility();
-      OnChanged();
-      break;
-
     default:
       NOTREACHED() << "Unexpected notification";
       break;
   }
 }
 
+void LocationBarViewMac::OnPreferenceChanged(PrefServiceBase* service,
+                                             const std::string& pref_name) {
+  UpdateStarDecorationVisibility();
+  OnChanged();
+}
+
 void LocationBarViewMac::PostNotification(NSString* notification) {
   [[NSNotificationCenter defaultCenter] postNotificationName:notification
                                         object:[NSValue valueWithPointer:this]];