Fix compilation error in mojo/shell/test_package_manager.h

mojo/shell/test_package_manager.h

 // Copyright 2015 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 MOJO_SHELL_TEST_PACKAGE_MANAGER_H_
 #define MOJO_SHELL_TEST_PACKAGE_MANAGER_H_
 
 #include <map>
 #include <string>
 
 #include "mojo/shell/package_manager.h"
 
 class GURL;
 
 namespace mojo {
 namespace shell {
 
 // An implementation of PackageManager used by tests to support content handler
 // registration for MIME types.
 class TestPackageManager : public PackageManager {
  public:
   TestPackageManager();
-  virtual ~TestPackageManager();
+  ~TestPackageManager() override;
 
   void RegisterContentHandler(const std::string& mime_type,
                               const GURL& content_handler_url);
 
  private:
   using MimeTypeToURLMap = std::map<std::string, GURL>;
 
   // Overridden from PackageManager:
   void SetApplicationManager(ApplicationManager* manager) override;
   GURL ResolveURL(const GURL& url) override;
   void FetchRequest(
       URLRequestPtr request,
       const Fetcher::FetchCallback& loader_callback) override;
   bool HandleWithContentHandler(Fetcher* fetcher,
                                 const GURL& unresolved_url,
                                 base::TaskRunner* task_runner,
                                 URLResponsePtr* new_response,
                                 GURL* content_handler_url,
                                 std::string* qualifier) override;
 
   MimeTypeToURLMap mime_type_to_url_;
 
   DISALLOW_COPY_AND_ASSIGN(TestPackageManager);
 };
 
 }  // namespace shell
 }  // namespace mojo
 
 #endif  // MOJO_SHELL_TEST_PACKAGE_MANAGER_H_