Add Hide and Show to the app list SearchBoxView.

ui/app_list/views/search_box_view_delegate.h

 // Copyright 2013 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 UI_APP_LIST_VIEWS_SEARCH_BOX_VIEW_DELEGATE_H_
 #define UI_APP_LIST_VIEWS_SEARCH_BOX_VIEW_DELEGATE_H_
 
 #include "ui/app_list/app_list_export.h"
 
 namespace app_list {
 
 class SearchBoxView;
 
 class APP_LIST_EXPORT SearchBoxViewDelegate {
  public:
   // Invoked when query text has changed by the user.
   virtual void QueryChanged(SearchBoxView* sender) = 0;
 
+  // Invoked when the view's visibility has been altered.
+  virtual void SearchBoxVisibilityChanged(SearchBoxView* sender) = 0;
+
  protected:
   virtual ~SearchBoxViewDelegate() {}
 };
 
 }  // namespace app_list
 
 #endif  // UI_APP_LIST_VIEWS_SEARCH_BOX_VIEW_DELEGATE_H_