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

components/test_runner/mock_web_user_media_client.h

Index: components/test_runner/mock_web_user_media_client.h
diff --git a/components/test_runner/mock_web_user_media_client.h b/components/test_runner/mock_web_user_media_client.h
index 1140086b3243e820827e4c191982f3afba9acb9a..dda0d4df31a92ae57a45abbba6f6e55b65801154 100644
--- a/components/test_runner/mock_web_user_media_client.h
+++ b/components/test_runner/mock_web_user_media_client.h
@@ -16,13 +16,13 @@ class WebTestDelegate;
 class MockWebUserMediaClient : public blink::WebUserMediaClient {
  public:
   explicit MockWebUserMediaClient(WebTestDelegate* delegate);
-  virtual ~MockWebUserMediaClient() {}
+  ~MockWebUserMediaClient() override {}
 
-  virtual void requestUserMedia(const blink::WebUserMediaRequest&);
-  virtual void cancelUserMediaRequest(const blink::WebUserMediaRequest&);
-  virtual void requestMediaDevices(const blink::WebMediaDevicesRequest&);
-  virtual void cancelMediaDevicesRequest(const blink::WebMediaDevicesRequest&);
-  virtual void requestSources(const blink::WebMediaStreamTrackSourcesRequest&);
+  void requestUserMedia(const blink::WebUserMediaRequest&) override;
+  void cancelUserMediaRequest(const blink::WebUserMediaRequest&) override;
+  void requestMediaDevices(const blink::WebMediaDevicesRequest&) override;
+  void cancelMediaDevicesRequest(const blink::WebMediaDevicesRequest&) override;
+  void requestSources(const blink::WebMediaStreamTrackSourcesRequest&) override;
 
   // Task related methods
   WebTaskList* mutable_task_list() { return &task_list_; }