tweak the focus rectangle of TrayBackgroundView objects

ash/common/system/tray/actionable_view.h

Index: ash/common/system/tray/actionable_view.h
diff --git a/ash/common/system/tray/actionable_view.h b/ash/common/system/tray/actionable_view.h
index c54040cdfeadde32c74d74bd2c8bdf8774d058ec..bcb71349e359a629453b054baf74b304a52115a6 100644
--- a/ash/common/system/tray/actionable_view.h
+++ b/ash/common/system/tray/actionable_view.h
@@ -43,7 +43,10 @@ class ASH_EXPORT ActionableView : public views::ButtonListener,
  protected:
   SystemTrayItem* owner() { return owner_; }
 
-  void OnPaintFocus(gfx::Canvas* canvas);
+  // Draws focus rectangle on the canvas.
+  // Default implementation draws the focus rectangle with certain inset and
+  // color. Subclasses can override to change the default settings.
+  virtual void OnPaintFocus(gfx::Canvas* canvas);
 
   // Returns the bounds to paint the focus rectangle in.
   virtual gfx::Rect GetFocusBounds();