Move the web dialogs code to src/ui/web_dialogs from src/chrome

chrome/browser/ui/webui/web_dialog_observer.h

-// Copyright (c) 2012 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_UI_WEBUI_WEB_DIALOG_OBSERVER_H_
-#define CHROME_BROWSER_UI_WEBUI_WEB_DIALOG_OBSERVER_H_
-#pragma once
-
-namespace content {
-class RenderViewHost;
-class WebUI;
-}
-
-// Implement this class to receive notifications.
-class WebDialogObserver {
- public:
-  // Invoked when a web dialog has been shown.
-  // |webui| is the WebUI with which the dialog is associated.
-  // |render_view_host| is the RenderViewHost for the shown dialog.
-  virtual void OnDialogShown(content::WebUI* webui,
-                             content::RenderViewHost* render_view_host) = 0;
-
- protected:
-  virtual ~WebDialogObserver() {}
-};
-
-#endif  // CHROME_BROWSER_UI_WEBUI_WEB_DIALOG_OBSERVER_H_