Remove content::NotificationObserver dependency from most Prefs code.

chrome/browser/ui/webui/ntp/ntp_resource_cache_android.cc

Index: chrome/browser/ui/webui/ntp/ntp_resource_cache_android.cc
diff --git a/chrome/browser/ui/webui/ntp/ntp_resource_cache_android.cc b/chrome/browser/ui/webui/ntp/ntp_resource_cache_android.cc
index 28b3dae1dea10606a0ff78345a9641f3190604b0..34214f8c7452ba63dcb89c115c400a5f0f67e53a 100644
--- a/chrome/browser/ui/webui/ntp/ntp_resource_cache_android.cc
+++ b/chrome/browser/ui/webui/ntp/ntp_resource_cache_android.cc
@@ -56,6 +56,11 @@ void NTPResourceCache::Observe(int type,
   // No notifications necessary in Android.
 }
 
+void NTPResourceCache::OnPreferenceChanged(PrefServiceBase* service,
+                                           const std::string& pref_name) {
+  // No notifications necessary in Android.
+}
+
 void NTPResourceCache::CreateNewTabHTML() {
   // TODO(estade): these strings should be defined in their relevant handlers
   // (in GetLocalizedValues) and should have more legible names.