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

components/test_runner/mock_web_media_stream_center.cc

Index: components/test_runner/mock_web_media_stream_center.cc
diff --git a/components/test_runner/mock_web_media_stream_center.cc b/components/test_runner/mock_web_media_stream_center.cc
index e63a91fdc02851f245615b939b944dea85882024..3c9206195f19eff75f14ad85d68c10d2f0ad9993 100644
--- a/components/test_runner/mock_web_media_stream_center.cc
+++ b/components/test_runner/mock_web_media_stream_center.cc
@@ -51,10 +51,10 @@ class MockWebAudioDestinationConsumer
     : public blink::WebAudioDestinationConsumer {
  public:
   MockWebAudioDestinationConsumer() {}
-  virtual ~MockWebAudioDestinationConsumer() {}
-  virtual void setFormat(size_t number_of_channels, float sample_rate) {}
-  virtual void consumeAudio(const blink::WebVector<const float*>&,
-                            size_t number_of_frames) {}
+  ~MockWebAudioDestinationConsumer() override {}
+  void setFormat(size_t number_of_channels, float sample_rate) override {}
+  void consumeAudio(const blink::WebVector<const float*>&,
+                    size_t number_of_frames) override {}
 
   DISALLOW_COPY_AND_ASSIGN(MockWebAudioDestinationConsumer);
 };