Clean up how we handle themes in the extensions system and management API....

chrome/browser/extensions/extension_management_api.h

Index: chrome/browser/extensions/extension_management_api.h
===================================================================
--- chrome/browser/extensions/extension_management_api.h	(revision 75613)
+++ chrome/browser/extensions/extension_management_api.h	(working copy)
@@ -6,7 +6,6 @@
 #define CHROME_BROWSER_EXTENSIONS_EXTENSION_MANAGEMENT_API_H__
 #pragma once
 
-#include "base/singleton.h"
 #include "chrome/browser/extensions/extension_function.h"
 #include "chrome/common/notification_observer.h"
 #include "chrome/common/notification_registrar.h"
@@ -50,18 +49,13 @@
 
 class ExtensionManagementEventRouter : public NotificationObserver {
  public:
-  // Get the singleton instance of the event router.
-  static ExtensionManagementEventRouter* GetInstance();
+  ExtensionManagementEventRouter();
+  virtual ~ExtensionManagementEventRouter();
 
-  // Performs one-time initialization of our singleton.
+  // Performs one-time initialization.
   void Init();
 
  private:
-  friend struct DefaultSingletonTraits<ExtensionManagementEventRouter>;
-
-  ExtensionManagementEventRouter();
-  virtual ~ExtensionManagementEventRouter();
-
   // NotificationObserver implementation.
   virtual void Observe(NotificationType type,
                        const NotificationSource& source,