Allow app list tiles to show search results in the experimental app list.

ui/app_list/search_result_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 UI_APP_LIST_SEARCH_RESULT_OBSERVER_H_
 #define UI_APP_LIST_SEARCH_RESULT_OBSERVER_H_
 
 #include "ui/app_list/app_list_export.h"
 
 namespace app_list {
 
 class APP_LIST_EXPORT SearchResultObserver {
  public:
   // Invoked when the SearchResult's icon has changed.
-  virtual void OnIconChanged() = 0;
+  virtual void OnIconChanged() {}
 
   // Invoked when the SearchResult's actions have changed.
-  virtual void OnActionsChanged() = 0;
+  virtual void OnActionsChanged() {}
 
   // Invoked when the SearchResult's is_installing flag has changed.
-  virtual void OnIsInstallingChanged() = 0;
+  virtual void OnIsInstallingChanged() {}
 
   // Invoked when the download percentage has changed.
-  virtual void OnPercentDownloadedChanged() = 0;
+  virtual void OnPercentDownloadedChanged() {}
 
   // Invoked when the item represented by the SearchResult is installed.
-  virtual void OnItemInstalled() = 0;
+  virtual void OnItemInstalled() {}
 
   // Invoked when the item represented by the SearchResult is uninstalled.
-  virtual void OnItemUninstalled() = 0;
+  virtual void OnItemUninstalled() {}
+
+  // Invoked just before the SearchResult is destroyed.
+  virtual void OnResultDestroying() {}
 
  protected:
   virtual ~SearchResultObserver() {}
 };
 
 }  // namespace app_list
 
 #endif  // UI_APP_LIST_SEARCH_RESULT_OBSERVER_H_