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

extensions/test/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 EXTENSIONS_TEST_EXTENSION_TEST_NOTIFICATION_OBSERVER_H_
 #define EXTENSIONS_TEST_EXTENSION_TEST_NOTIFICATION_OBSERVER_H_
 
 #include <memory>
 #include <string>
 
 #include "base/callback.h"
 #include "base/callback_list.h"
 #include "base/macros.h"
 #include "base/scoped_observer.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 #include "extensions/browser/process_manager_observer.h"
 
 namespace content {
 class BrowserContext;
 class NotificationDetails;
 class WindowedNotificationObserver;
 }
 
 namespace extensions {
 class ProcessManager;
-}
 
 // Test helper class for observing extension-related events.
 class ExtensionTestNotificationObserver : public content::NotificationObserver {
  public:
   explicit ExtensionTestNotificationObserver(content::BrowserContext* context);
   ~ExtensionTestNotificationObserver() override;
 
   // Wait for an extension install error to be raised. Returns true if an
   // error was raised.
   bool WaitForExtensionInstallError();
@@ skipping 94 matching lines @@
   // The condition for which we are waiting. This should be checked in any
   // observing methods that could trigger it.
   base::Callback<bool(void)> condition_;
 
   // The closure to quit the currently-running message loop.
   base::Closure quit_closure_;
 
   DISALLOW_COPY_AND_ASSIGN(ExtensionTestNotificationObserver);
 };
 
+}  // namespace extensions
+
 #endif  // EXTENSIONS_TEST_EXTENSION_TEST_NOTIFICATION_OBSERVER_H_