Remove content::NotificationObserver dependency from most Prefs code.

chrome/browser/ui/webui/options/chromeos/core_chromeos_options_handler.h

Index: chrome/browser/ui/webui/options/chromeos/core_chromeos_options_handler.h
diff --git a/chrome/browser/ui/webui/options/chromeos/core_chromeos_options_handler.h b/chrome/browser/ui/webui/options/chromeos/core_chromeos_options_handler.h
index 82b9298f07f4b2cc4aec1d3abe4e51e48a7342dc..a4b37d46ef5c53ad36ce0464971ed59ef77f50bc 100644
--- a/chrome/browser/ui/webui/options/chromeos/core_chromeos_options_handler.h
+++ b/chrome/browser/ui/webui/options/chromeos/core_chromeos_options_handler.h
@@ -8,13 +8,15 @@
 #include "base/compiler_specific.h"
 #include "base/memory/weak_ptr.h"
 #include "base/prefs/public/pref_change_registrar.h"
+#include "base/prefs/public/pref_observer.h"
 #include "chrome/browser/ui/webui/options/core_options_handler.h"
 
 namespace chromeos {
 namespace options {
 
 // CoreChromeOSOptionsHandler handles ChromeOS settings.
-class CoreChromeOSOptionsHandler : public ::options::CoreOptionsHandler {
+class CoreChromeOSOptionsHandler
+    : public ::options::CoreOptionsHandler {
  public:
   CoreChromeOSOptionsHandler();
   virtual ~CoreChromeOSOptionsHandler();
@@ -37,6 +39,10 @@ class CoreChromeOSOptionsHandler : public ::options::CoreOptionsHandler {
                        const content::NotificationSource& source,
                        const content::NotificationDetails& details) OVERRIDE;
 
+  // PrefObserver implementation.
+  virtual void OnPreferenceChanged(PrefServiceBase* service,
+                                   const std::string& pref_name) OVERRIDE;
+
  private:
   // Notifies registered JS callbacks on ChromeOS setting change.
   void NotifySettingsChanged(const std::string* setting_name);