Remove content::NotificationObserver dependency from most Prefs code.

chrome/browser/prefs/scoped_user_pref_update_unittest.cc

Index: chrome/browser/prefs/scoped_user_pref_update_unittest.cc
diff --git a/chrome/browser/prefs/scoped_user_pref_update_unittest.cc b/chrome/browser/prefs/scoped_user_pref_update_unittest.cc
index 98ffc894199deec2b483c424f8435d9df16e264c..f5e6927bd0b2c7260f160df1beb6d952d8784b21 100644
--- a/chrome/browser/prefs/scoped_user_pref_update_unittest.cc
+++ b/chrome/browser/prefs/scoped_user_pref_update_unittest.cc
@@ -42,7 +42,7 @@ TEST_F(ScopedUserPrefUpdateTest, RegularUse) {
   expected_dictionary.SetString(kKey, kValue);
 
   {
-    EXPECT_CALL(observer_, Observe(_, _, _)).Times(0);
+    EXPECT_CALL(observer_, OnPreferenceChanged(_, _)).Times(0);
     DictionaryPrefUpdate update(&prefs_, kPref);
     DictionaryValue* value = update.Get();
     ASSERT_TRUE(value);
@@ -69,7 +69,7 @@ TEST_F(ScopedUserPrefUpdateTest, RegularUse) {
 
 TEST_F(ScopedUserPrefUpdateTest, NeverTouchAnything) {
   const DictionaryValue* old_value = prefs_.GetDictionary(kPref);
-  EXPECT_CALL(observer_, Observe(_, _, _)).Times(0);
+  EXPECT_CALL(observer_, OnPreferenceChanged(_, _)).Times(0);
   {
     DictionaryPrefUpdate update(&prefs_, kPref);
   }