Fix classes that have too many virtuals for inline constructors.

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 15 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() {}
 
  protected:
+  SearchResultObserver() = default;
   virtual ~SearchResultObserver() {}
 };
 
 }  // namespace app_list
 
 #endif  // UI_APP_LIST_SEARCH_RESULT_OBSERVER_H_