Enforce marking "override" for functions overriding Blink in components/test_runner/.

components/test_runner/mock_web_audio_device.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 COMPONENTS_TEST_RUNNER_MOCK_WEB_AUDIO_DEVICE_H_
 #define COMPONENTS_TEST_RUNNER_MOCK_WEB_AUDIO_DEVICE_H_
 
 #include "base/macros.h"
 #include "third_party/WebKit/public/platform/WebAudioDevice.h"
 
 namespace test_runner {
 
 class MockWebAudioDevice : public blink::WebAudioDevice {
  public:
   explicit MockWebAudioDevice(double sample_rate);
-  virtual ~MockWebAudioDevice();
+  ~MockWebAudioDevice() override;
 
   // blink::WebAudioDevice:
-  virtual void start();
-  virtual void stop();
-  virtual double sampleRate();
+  void start() override;
+  void stop() override;
+  double sampleRate() override;
 
  private:
   double sample_rate_;
 
   DISALLOW_COPY_AND_ASSIGN(MockWebAudioDevice);
 };
 
 }  // namespace test_runner
 
 #endif  // COMPONENTS_TEST_RUNNER_MOCK_WEB_AUDIO_DEVICE_H_