Standardize usage of virtual/override/final specifiers.

extensions/shell/test/shell_apitest.h

 // Copyright 2014 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 EXTENSIONS_SHELL_TEST_SHELL_API_TEST_H_
 #define EXTENSIONS_SHELL_TEST_SHELL_API_TEST_H_
 
 #include <string>
 
 #include "extensions/shell/test/shell_test.h"
 
 namespace extensions {
 
 // Base class for app shell browser API tests that load an app/extension
 // and wait for a success message from the chrome.test API.
 class ShellApiTest : public AppShellTest {
  public:
   ShellApiTest();
-  virtual ~ShellApiTest();
+  ~ShellApiTest() override;
 
   // Loads an unpacked platform app from a directory using the current
   // ExtensionSystem, launches it, and waits for a chrome.test success
   // notification. Returns true if the test succeeds. |app_dir| is a
   // subpath under extensions/test/data.
   bool RunAppTest(const std::string& app_dir);
 
  protected:
   // If it failed, what was the error message?
   std::string message_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ShellApiTest);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_SHELL_TEST_SHELL_API_TEST_H_