Update {virtual,override} to follow C++11 style in content.

content/public/test/mock_render_thread.h

Index: content/public/test/mock_render_thread.h
diff --git a/content/public/test/mock_render_thread.h b/content/public/test/mock_render_thread.h
index 95d7be8887db880b11f35e4d82fe786f556b5d8d..3623ab599dc1395772330b127049aa18bf1e7559 100644
--- a/content/public/test/mock_render_thread.h
+++ b/content/public/test/mock_render_thread.h
@@ -71,8 +71,8 @@ class MockRenderThread : public RenderThread {
   bool ResolveProxy(const GURL& url, std::string* proxy_list) override;
   base::WaitableEvent* GetShutdownEvent() override;
 #if defined(OS_WIN)
-  virtual void PreCacheFont(const LOGFONT& log_font) override;
-  virtual void ReleaseCachedFonts() override;
+  void PreCacheFont(const LOGFONT& log_font) override;
+  void ReleaseCachedFonts() override;
 #endif
   ServiceRegistry* GetServiceRegistry() override;