Remove content::NotificationObserver dependency from most Prefs code.

chrome/browser/prefs/pref_observer_mock.cc

Index: chrome/browser/prefs/pref_observer_mock.cc
diff --git a/chrome/browser/prefs/pref_observer_mock.cc b/chrome/browser/prefs/pref_observer_mock.cc
index d42c69c418bf707dd4665c237a086f96291f606f..0b3f82ad7dbed15771e9c50361ccdcb1f466086e 100644
--- a/chrome/browser/prefs/pref_observer_mock.cc
+++ b/chrome/browser/prefs/pref_observer_mock.cc
@@ -9,12 +9,9 @@ PrefObserverMock::PrefObserverMock() {}
 
 PrefObserverMock::~PrefObserverMock() {}
 
-void PrefObserverMock::Expect(const PrefService* prefs,
+void PrefObserverMock::Expect(PrefServiceBase* prefs,
                               const std::string& pref_name,
                               const Value* value) {
-  EXPECT_CALL(*this, Observe(int(chrome::NOTIFICATION_PREF_CHANGED),
-                             content::Source<PrefService>(prefs),
-                             Property(&content::Details<std::string>::ptr,
-                                      Pointee(pref_name))))
+  EXPECT_CALL(*this, OnPreferenceChanged(prefs, pref_name))
       .With(PrefValueMatches(prefs, pref_name, value));
 }