Remove content::NotificationObserver dependency from most Prefs code.

chrome/browser/ui/cocoa/browser_window_cocoa_unittest.mm

Index: chrome/browser/ui/cocoa/browser_window_cocoa_unittest.mm
diff --git a/chrome/browser/ui/cocoa/browser_window_cocoa_unittest.mm b/chrome/browser/ui/cocoa/browser_window_cocoa_unittest.mm
index e5814f863b6d9fcd7c9c99463d4911134d13a87d..318fa8bc1c20466027f30ca04860ef51dfdde728 100644
--- a/chrome/browser/ui/cocoa/browser_window_cocoa_unittest.mm
+++ b/chrome/browser/ui/cocoa/browser_window_cocoa_unittest.mm
@@ -4,6 +4,7 @@
 
 #include "base/memory/scoped_nsobject.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/prefs/public/pref_observer.h"
 #include "base/string_util.h"
 #include "chrome/browser/bookmarks/bookmark_utils.h"
 #import "chrome/browser/ui/cocoa/browser_window_cocoa.h"
@@ -19,7 +20,7 @@
 // A BrowserWindowCocoa that goes PONG when
 // BOOKMARK_BAR_VISIBILITY_PREF_CHANGED is sent.  This is so we can be
 // sure we are observing it.
-class BrowserWindowCocoaPong : public BrowserWindowCocoa {
+class BrowserWindowCocoaPong : public BrowserWindowCocoa, public PrefObserver {
  public:
   BrowserWindowCocoaPong(Browser* browser,
                          BrowserWindowController* controller)
@@ -28,18 +29,13 @@ class BrowserWindowCocoaPong : public BrowserWindowCocoa {
   }
   virtual ~BrowserWindowCocoaPong() { }
 
-  void Observe(int type,
-               const content::NotificationSource& source,
-               const content::NotificationDetails& details) {
-    if (type == chrome::NOTIFICATION_PREF_CHANGED) {
-      const std::string& pref_name =
-          *content::Details<std::string>(details).ptr();
-      if (pref_name == prefs::kShowBookmarkBar)
-        pong_ = true;
-    }
-    BrowserWindowCocoa::Observe(type, source, details);
+  virtual void OnPreferenceChanged(PrefServiceBase* service,
+                                   const std::string& pref_name) OVERRIDE {
+    if (pref_name == prefs::kShowBookmarkBar)
+      pong_ = true;
   }
 
+
   bool pong_;
 };