Remove content::NotificationObserver dependency from most Prefs code.

chrome/browser/printing/cloud_print/cloud_print_proxy_service.cc

Index: chrome/browser/printing/cloud_print/cloud_print_proxy_service.cc
diff --git a/chrome/browser/printing/cloud_print/cloud_print_proxy_service.cc b/chrome/browser/printing/cloud_print/cloud_print_proxy_service.cc
index 49dadfb1ee1dd8e9ed9a9b6efbee1612671c94b6..18ed40dfa27f60df8c1bf8dff464806f4e87aae2 100644
--- a/chrome/browser/printing/cloud_print/cloud_print_proxy_service.cc
+++ b/chrome/browser/printing/cloud_print/cloud_print_proxy_service.cc
@@ -207,11 +207,8 @@ void CloudPrintProxyService::OnCloudPrintSetupClosed() {
       FROM_HERE, base::Bind(&browser::EndKeepAlive));
 }
 
-void CloudPrintProxyService::Observe(
-    int type,
-    const content::NotificationSource& source,
-    const content::NotificationDetails& details) {
-  DCHECK_EQ(chrome::NOTIFICATION_PREF_CHANGED, type);
+void CloudPrintProxyService::OnPreferenceChanged(PrefServiceBase* service,
+                                                 const std::string& pref_name) {
   ApplyCloudPrintConnectorPolicy();
 }