[MD] simplify and unify some ink drop center calculations

ui/views/controls/button/label_button.h

Index: ui/views/controls/button/label_button.h
diff --git a/ui/views/controls/button/label_button.h b/ui/views/controls/button/label_button.h
index eee771e79222b726ee2fa2dfb309279675a0893b..9d6b9d359309bd24096243302c925bd703b2f04d 100644
--- a/ui/views/controls/button/label_button.h
+++ b/ui/views/controls/button/label_button.h
@@ -105,6 +105,7 @@ class VIEWS_EXPORT LabelButton : public CustomButton,
   void RemoveInkDropLayer(ui::Layer* ink_drop_layer) override;
   scoped_ptr<InkDropAnimation> CreateInkDropAnimation() const override;
   scoped_ptr<InkDropHover> CreateInkDropHover() const override;
+  gfx::Point GetInkDropCenter() const override;
 
  protected:
   ImageView* image() const { return image_; }