Standardize usage of virtual/override/final specifiers.

ash/wm/overview/window_selector.cc

Index: ash/wm/overview/window_selector.cc
diff --git a/ash/wm/overview/window_selector.cc b/ash/wm/overview/window_selector.cc
index c2b99d1e3ec233a4ca39c36850a2c1f543f1dcc3..15723c557f339345d3bbe71742afee7ed9c5c4b4 100644
--- a/ash/wm/overview/window_selector.cc
+++ b/ash/wm/overview/window_selector.cc
@@ -119,9 +119,9 @@ class RoundedContainerView : public views::View {
         background_(background) {
   }
 
-  virtual ~RoundedContainerView() {}
+  ~RoundedContainerView() override {}
 
-  virtual void OnPaint(gfx::Canvas* canvas) override {
+  void OnPaint(gfx::Canvas* canvas) override {
     views::View::OnPaint(canvas);
 
     SkScalar radius = SkIntToScalar(corner_radius_);