Warn on missing OVERRIDE/virtual everywhere, not just in header files.

content/renderer/dom_serializer_browsertest.cc

Index: content/renderer/dom_serializer_browsertest.cc
diff --git a/content/renderer/dom_serializer_browsertest.cc b/content/renderer/dom_serializer_browsertest.cc
index 0e841430c7d7ee5400662acdcc1083b64163d42c..3df004d560ff66653d889449df37c66fe48d1b46 100644
--- a/content/renderer/dom_serializer_browsertest.cc
+++ b/content/renderer/dom_serializer_browsertest.cc
@@ -151,7 +151,7 @@ class LoadObserver : public RenderViewObserver {
       : RenderViewObserver(render_view),
         quit_closure_(quit_closure) {}
 
-  virtual void DidFinishLoad(WebKit::WebFrame* frame) {
+  virtual void DidFinishLoad(WebKit::WebFrame* frame) OVERRIDE {
     if (frame == render_view()->GetWebView()->mainFrame())
       quit_closure_.Run();
   }
@@ -167,7 +167,7 @@ class DomSerializerTests : public ContentBrowserTest,
     : serialized_(false),
       local_directory_name_(FILE_PATH_LITERAL("./dummy_files/")) {}
 
-  virtual void SetUpCommandLine(CommandLine* command_line) {
+  virtual void SetUpCommandLine(CommandLine* command_line) OVERRIDE {
     command_line->AppendSwitch(switches::kSingleProcess);
 #if defined(OS_WIN) && defined(USE_AURA)
     // Don't want to try to create a GPU process.