RefCounted types should not have public destructors, delegate cleanup

chrome/browser/download/download_extension_api.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_DOWNLOAD_DOWNLOAD_EXTENSION_API_H_
 #define CHROME_BROWSER_DOWNLOAD_DOWNLOAD_EXTENSION_API_H_
 #pragma once
 
 #include <map>
 #include <set>
@@ skipping 49 matching lines @@
     DOWNLOADS_FUNCTION_SET_DESTINATION = 6,
     DOWNLOADS_FUNCTION_ACCEPT_DANGER = 7,
     DOWNLOADS_FUNCTION_SHOW = 8,
     DOWNLOADS_FUNCTION_DRAG = 9,
     DOWNLOADS_FUNCTION_GET_FILE_ICON = 10,
     // Insert new values here, not at the beginning.
     DOWNLOADS_FUNCTION_LAST
   };
 
  protected:
+  virtual ~DownloadsFunctionInterface() {}
+
   // Return true if args_ is well-formed, otherwise set error_ and return false.
   virtual bool ParseArgs() = 0;
 
   // Implementation-specific logic. "Do the thing that you do."  Should return
   // true if the call succeeded and false otherwise.
   virtual bool RunInternal() = 0;
 
   // Which subclass is this.
   virtual DownloadsFunctionName function() const = 0;
 
@@ skipping 296 matching lines @@
   content::DownloadManager* manager_;
   ItemMap downloads_;
   ItemJsonMap item_jsons_;
   STLValueDeleter<ItemJsonMap> delete_item_jsons_;
   OnChangedStatMap on_changed_stats_;
   STLValueDeleter<OnChangedStatMap> delete_on_changed_stats_;
 
   DISALLOW_COPY_AND_ASSIGN(ExtensionDownloadsEventRouter);
 };
 #endif  // CHROME_BROWSER_DOWNLOAD_DOWNLOAD_EXTENSION_API_H_