Standardize usage of virtual/override/final in tools/gn/

tools/gn/action_target_generator.h

Index: tools/gn/action_target_generator.h
diff --git a/tools/gn/action_target_generator.h b/tools/gn/action_target_generator.h
index 9f3e22448ca17b3da06f86cf869694e79079d302..668f45908e43b6f25a207f39a2eb62553ec7c9b1 100644
--- a/tools/gn/action_target_generator.h
+++ b/tools/gn/action_target_generator.h
@@ -19,7 +19,7 @@ class ActionTargetGenerator : public TargetGenerator {
   virtual ~ActionTargetGenerator();

[Peter Kasting, 2014/10/21 22:47:51]

Shouldn't this be "override" instead of "virtual"?

[dcheng, 2014/10/21 22:57:15]

Yeah. I'm not sure why, but the plugin is currently missing some cases. =/

I'm going to be investigating this--I'm guessing one of the early returns is
somehow getting triggered, but I'm not yet sure how.

[viettrungluu, 2014/10/22 00:42:14]

It's not missing it: the base class's dtor isn't virtual, so this is really a
bug in the code.

(Quite possibly, we should have a warning/error when a subclass has a virtual
dtor but the superclass doesn't.[*])

[*] At least when the superclass has an explicitly-declared dtor. Sometimes we
declare interfaces without providing dtors, which is somewhat debatable.[**]

[**] Arguably, in such cases, the interface should have a protected, but
possibly non-virtual dtor.

 
  protected:
-  virtual void DoRun() OVERRIDE;
+  void DoRun() OVERRIDE;
 
  private:
   bool FillScript();