[Extensions] Move [Chrome]ExtensionTestNotificationObserver into extensions::

chrome/browser/extensions/chrome_extension_test_notification_observer.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_EXTENSIONS_CHROME_EXTENSION_TEST_NOTIFICATION_OBSERVER_H_
 #define CHROME_BROWSER_EXTENSIONS_CHROME_EXTENSION_TEST_NOTIFICATION_OBSERVER_H_
 
 #include <string>
 
 #include "base/macros.h"
 #include "chrome/browser/extensions/api/extension_action/extension_action_api.h"
 #include "extensions/test/extension_test_notification_observer.h"
 
 class Browser;
 
 namespace content {
 class BrowserContext;
 }
 
+namespace extensions {
+
 // Test helper class for observing extension-related events.
-// TODO(devlin): This should be in the extensions namespace.
 class ChromeExtensionTestNotificationObserver
     : public ExtensionTestNotificationObserver,
-      public extensions::ExtensionActionAPI::Observer {
+      public ExtensionActionAPI::Observer {
  public:
   explicit ChromeExtensionTestNotificationObserver(Browser* browser);
   explicit ChromeExtensionTestNotificationObserver(
       content::BrowserContext* browser_context);
   ~ChromeExtensionTestNotificationObserver() override;
 
   // Waits for the number of visible page actions to change to |count|.
   bool WaitForPageActionVisibilityChangeTo(int count);
 
   // Waits until an extension is loaded and all view have loaded.
   void WaitForExtensionAndViewLoad();
 
   // Waits for all extension views to load.
   bool WaitForExtensionViewsToLoad();
 
   // Waits for extension to be idle.
   bool WaitForExtensionIdle(const std::string& extension_id);
 
   // Waits for extension to be not idle.
   bool WaitForExtensionNotIdle(const std::string& extension_id);
 
  private:
   content::BrowserContext* GetBrowserContext();
 
-  // extensions::ExtensionActionAPI::Observer:
+  // ExtensionActionAPI::Observer:
   void OnPageActionsUpdated(content::WebContents* contents) override;
 
   Browser* browser_;
 
   DISALLOW_COPY_AND_ASSIGN(ChromeExtensionTestNotificationObserver);
 };
 
+}  // namespace extensions
+
 #endif  // CHROME_BROWSER_EXTENSIONS_CHROME_EXTENSION_TEST_NOTIFICATION_OBSERVER_H_