Remove content::NotificationObserver dependency from most Prefs code.

chrome/browser/ui/webui/ntp/ntp_resource_cache.h

Index: chrome/browser/ui/webui/ntp/ntp_resource_cache.h
diff --git a/chrome/browser/ui/webui/ntp/ntp_resource_cache.h b/chrome/browser/ui/webui/ntp/ntp_resource_cache.h
index c4a57b1461d4e6a43f8fa6425790e05ee6ffbc2d..856964942ab17e65e829c4ab3ba710237ef6aea4 100644
--- a/chrome/browser/ui/webui/ntp/ntp_resource_cache.h
+++ b/chrome/browser/ui/webui/ntp/ntp_resource_cache.h
@@ -9,6 +9,7 @@
 #include "base/compiler_specific.h"
 #include "base/memory/ref_counted.h"
 #include "base/prefs/public/pref_change_registrar.h"
+#include "base/prefs/public/pref_observer.h"
 #include "base/string16.h"
 #include "chrome/browser/profiles/profile_keyed_service.h"
 #include "content/public/browser/notification_observer.h"
@@ -27,6 +28,7 @@ class ThemeProvider;
 // This class keeps a cache of NTP resources (HTML and CSS) so we don't have to
 // regenerate them all the time.
 class NTPResourceCache : public content::NotificationObserver,
+                         public PrefObserver,
                          public ProfileKeyedService {
  public:
   explicit NTPResourceCache(Profile* profile);
@@ -40,6 +42,10 @@ class NTPResourceCache : public content::NotificationObserver,
                        const content::NotificationSource& source,
                        const content::NotificationDetails& details) OVERRIDE;
 
+  // PrefObserver interface.
+  virtual void OnPreferenceChanged(PrefServiceBase* service,
+                                   const std::string& pref_name) OVERRIDE;
+
   // Returns the CSS background-position-y style for new_tab_theme.css:
   // - |y_pos| is the vertical offset of theme image in content view.
   // - |alignment| is alignment of theme image.