Remove content::NotificationObserver dependency from most Prefs code.

chrome/browser/printing/print_view_manager.cc

Index: chrome/browser/printing/print_view_manager.cc
diff --git a/chrome/browser/printing/print_view_manager.cc b/chrome/browser/printing/print_view_manager.cc
index 56c58ca6693a47510f67eb722bcff7707cb36b10..cad5695004979547065700eee863ec5f7a757cba 100644
--- a/chrome/browser/printing/print_view_manager.cc
+++ b/chrome/browser/printing/print_view_manager.cc
@@ -389,10 +389,6 @@ void PrintViewManager::Observe(int type,
       OnNotifyPrintJobEvent(*content::Details<JobEventDetails>(details).ptr());
       break;
     }
-    case chrome::NOTIFICATION_PREF_CHANGED: {
-      UpdateScriptedPrintingBlocked();
-      break;
-    }
     case chrome::NOTIFICATION_CONTENT_BLOCKED_STATE_CHANGED: {
       tab_content_blocked_ = *content::Details<const bool>(details).ptr();
       UpdateScriptedPrintingBlocked();
@@ -405,6 +401,11 @@ void PrintViewManager::Observe(int type,
   }
 }
 
+void PrintViewManager::OnPreferenceChanged(PrefServiceBase* service,
+                                           const std::string& pref_name) {
+  UpdateScriptedPrintingBlocked();
+}
+
 void PrintViewManager::OnNotifyPrintJobEvent(
     const JobEventDetails& event_details) {
   switch (event_details.type()) {