Remove content::NotificationObserver dependency from most Prefs code.

chrome/browser/plugins/plugin_status_pref_setter.h

Index: chrome/browser/plugins/plugin_status_pref_setter.h
diff --git a/chrome/browser/plugins/plugin_status_pref_setter.h b/chrome/browser/plugins/plugin_status_pref_setter.h
index ab406ae891a7ccc27f4892c455f7947dfceef4bd..915a8205097646836d50561ee9cbc0fb865e74f6 100644
--- a/chrome/browser/plugins/plugin_status_pref_setter.h
+++ b/chrome/browser/plugins/plugin_status_pref_setter.h
@@ -9,6 +9,7 @@
 
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
+#include "base/prefs/public/pref_observer.h"
 #include "chrome/browser/api/prefs/pref_member.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
@@ -34,8 +35,7 @@ class PluginStatusPrefSetter : public content::NotificationObserver {
   // any value changes.
   // This asynchronously calls the PluginService to get the list of installed
   // plug-ins.
-  void Init(Profile* profile,
-            content::NotificationObserver* observer);
+  void Init(Profile* profile, PrefObserver* observer);
 
   bool IsClearPluginLSODataEnabled() const {
     return clear_plugin_lso_data_enabled_.GetValue();