Remove content::NotificationObserver dependency from most Prefs code.

chrome/browser/content_settings/cookie_settings.cc

Index: chrome/browser/content_settings/cookie_settings.cc
diff --git a/chrome/browser/content_settings/cookie_settings.cc b/chrome/browser/content_settings/cookie_settings.cc
index 72cfd1709f9fd9c588357e39dc116ef88afbfd83..d47eecd7d46ee8d6beea512d2a868e4a1f917539 100644
--- a/chrome/browser/content_settings/cookie_settings.cc
+++ b/chrome/browser/content_settings/cookie_settings.cc
@@ -155,24 +155,17 @@ void CookieSettings::ResetCookieSetting(
       CONTENT_SETTING_DEFAULT);
 }
 
-void CookieSettings::Observe(int type,
-                             const content::NotificationSource& source,
-                             const content::NotificationDetails& details) {
+void CookieSettings::OnPreferenceChanged(PrefServiceBase* prefs,
+                                         const std::string& name) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
-  if (type == chrome::NOTIFICATION_PREF_CHANGED) {
-    PrefService* prefs = content::Source<PrefService>(source).ptr();
-    std::string* name = content::Details<std::string>(details).ptr();
-    if (*name == prefs::kBlockThirdPartyCookies) {
-      base::AutoLock auto_lock(lock_);
-      block_third_party_cookies_ = prefs->GetBoolean(
-          prefs::kBlockThirdPartyCookies);
-    } else {
-      NOTREACHED() << "Unexpected preference observed";
-      return;
-    }
+  if (name == prefs::kBlockThirdPartyCookies) {
+    base::AutoLock auto_lock(lock_);
+    block_third_party_cookies_ = prefs->GetBoolean(
+        prefs::kBlockThirdPartyCookies);
   } else {
-    NOTREACHED() << "Unexpected notification";
+    NOTREACHED() << "Unexpected preference observed";
+    return;
   }
 }