Remove content::NotificationObserver dependency from most Prefs code.

chrome/browser/ui/views/toolbar_view.cc

Index: chrome/browser/ui/views/toolbar_view.cc
diff --git a/chrome/browser/ui/views/toolbar_view.cc b/chrome/browser/ui/views/toolbar_view.cc
index 31076d13b6af5d8a4ee97d9fb95bc397bb40f7cc..7f91d3f070787f22b800dcf15da894ce5ab21c7f 100644
--- a/chrome/browser/ui/views/toolbar_view.cc
+++ b/chrome/browser/ui/views/toolbar_view.cc
@@ -528,14 +528,6 @@ void ToolbarView::Observe(int type,
                           const content::NotificationSource& source,
                           const content::NotificationDetails& details) {
   switch (type) {
-    case chrome::NOTIFICATION_PREF_CHANGED: {
-      std::string* pref_name = content::Details<std::string>(details).ptr();
-      if (*pref_name == prefs::kShowHomeButton) {
-        Layout();
-        SchedulePaint();
-      }
-      break;
-    }
     case chrome::NOTIFICATION_UPGRADE_RECOMMENDED:
     case chrome::NOTIFICATION_MODULE_INCOMPATIBILITY_BADGE_CHANGE:
     case chrome::NOTIFICATION_GLOBAL_ERRORS_CHANGED:
@@ -551,6 +543,14 @@ void ToolbarView::Observe(int type,
   }
 }
 
+void ToolbarView::OnPreferenceChanged(PrefServiceBase* service,
+                                      const std::string& pref_name) {
+  if (pref_name == prefs::kShowHomeButton) {
+    Layout();
+    SchedulePaint();
+  }
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // ToolbarView, ui::AcceleratorProvider implementation: