Implementing answer card hover highlight.

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 {
@@ skipping 14 matching lines @@
 
   // Invoked when the download percentage has changed.
   virtual void OnPercentDownloadedChanged() {}
 
   // Invoked when the item represented by the SearchResult is installed.
   virtual void OnItemInstalled() {}
 
   // Invoked just before the SearchResult is destroyed.
   virtual void OnResultDestroying() {}
 
+  // Invoked when SearchResult has an associated view, and the mouse cursor
+  // enters or exits that view.

[xiyuan, 2017/06/06 18:53:53]

nit: Document that it is needed because the view is views::WebView and existing
views mouse enter/exit events does not fire on it.

[vadimt, 2017/06/06 19:18:54]

Done.

+  virtual void OnViewHoverStateChanged() {}
+
  protected:
   virtual ~SearchResultObserver() {}
 };
 
 }  // namespace app_list
 
 #endif  // UI_APP_LIST_SEARCH_RESULT_OBSERVER_H_