Remove content::NotificationObserver dependency from most Prefs code.

chrome/browser/speech/chrome_speech_recognition_preferences.cc

Index: chrome/browser/speech/chrome_speech_recognition_preferences.cc
diff --git a/chrome/browser/speech/chrome_speech_recognition_preferences.cc b/chrome/browser/speech/chrome_speech_recognition_preferences.cc
index f5ef511ceada6f1a641923e2f1f7e7fb96818fb1..fc057fe6aff632b0a2fdf646dabde4bcfc1c39b6 100644
--- a/chrome/browser/speech/chrome_speech_recognition_preferences.cc
+++ b/chrome/browser/speech/chrome_speech_recognition_preferences.cc
@@ -141,14 +141,11 @@ void ChromeSpeechRecognitionPreferences::DetachFromProfile() {
   profile_ = NULL;
 }
 
-void ChromeSpeechRecognitionPreferences::Observe(
-    int type,
-    const content::NotificationSource& source,
-    const content::NotificationDetails& details) {
+void ChromeSpeechRecognitionPreferences::OnPreferenceChanged(
+    PrefServiceBase* service,
+    const std::string& pref_name) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-  DCHECK_EQ(type, chrome::NOTIFICATION_PREF_CHANGED);
-  std::string* pref_name = content::Details<std::string>(details).ptr();
-  ReloadPreference(*pref_name);
+  ReloadPreference(pref_name);
 }
 
 bool ChromeSpeechRecognitionPreferences::FilterProfanities() const {