Remove content::NotificationObserver dependency from most Prefs code.

chrome/browser/ui/browser_instant_controller.cc

Index: chrome/browser/ui/browser_instant_controller.cc
diff --git a/chrome/browser/ui/browser_instant_controller.cc b/chrome/browser/ui/browser_instant_controller.cc
index 66defb10d8d239e2f87abf13e18a963fd2306556..5f6319a20a723473ec04f7b616e70253f36d7fe6 100644
--- a/chrome/browser/ui/browser_instant_controller.cc
+++ b/chrome/browser/ui/browser_instant_controller.cc
@@ -104,15 +104,12 @@ TabContents* BrowserInstantController::GetActiveTabContents() const {
 }
 
 ////////////////////////////////////////////////////////////////////////////////
-// BrowserInstantController, content::NotificationObserver implementation:
-
-void BrowserInstantController::Observe(
-    int type,
-    const content::NotificationSource& source,
-    const content::NotificationDetails& details) {
-  DCHECK_EQ(chrome::NOTIFICATION_PREF_CHANGED, type);
-  DCHECK_EQ(std::string(prefs::kInstantEnabled),
-            *content::Details<std::string>(details).ptr());
+// BrowserInstantController, PrefObserver implementation:
+
+void BrowserInstantController::OnPreferenceChanged(
+    PrefServiceBase* service,
+    const std::string& pref_name) {
+  DCHECK_EQ(std::string(prefs::kInstantEnabled), pref_name);
   ResetInstant();
 }