Remove content::NotificationObserver dependency from most Prefs code.

chrome/browser/ui/browser.h

Index: chrome/browser/ui/browser.h
diff --git a/chrome/browser/ui/browser.h b/chrome/browser/ui/browser.h
index c74aadd8b3e4874af29b7ce10f2044c3850dad19..520358678c7b44debdfe0b519a67a9913b5e5ed6 100644
--- a/chrome/browser/ui/browser.h
+++ b/chrome/browser/ui/browser.h
@@ -16,6 +16,7 @@
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
 #include "base/prefs/public/pref_change_registrar.h"
+#include "base/prefs/public/pref_observer.h"
 #include "base/string16.h"
 #include "chrome/browser/api/prefs/pref_member.h"
 #include "chrome/browser/debugger/devtools_toggle_action.h"
@@ -36,6 +37,7 @@
 #include "chrome/common/content_settings.h"
 #include "chrome/common/content_settings_types.h"
 #include "chrome/common/extensions/extension_constants.h"
+#include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 #include "content/public/browser/page_navigator.h"
 #include "content/public/browser/web_contents_delegate.h"
@@ -106,6 +108,7 @@ class Browser : public TabStripModelObserver,
                 public ZoomObserver,
                 public content::PageNavigator,
                 public content::NotificationObserver,
+                public PrefObserver,
                 public ui::SelectFileDialog::Listener,
                 public chrome::search::SearchModelObserver {
  public:
@@ -689,6 +692,10 @@ class Browser : public TabStripModelObserver,
                        const content::NotificationSource& source,
                        const content::NotificationDetails& details) OVERRIDE;
 
+  // Overridden from PrefObserver:
+  virtual void OnPreferenceChanged(PrefServiceBase* service,
+                                   const std::string& pref_name) OVERRIDE;
+
   // Overridden from chrome::search::SearchModelObserver:
   virtual void ModeChanged(const chrome::search::Mode& old_mode,
                            const chrome::search::Mode& new_mode) OVERRIDE;