Adding ripple effect for clicks on MD slider

ui/views/controls/md_slider.h

Index: ui/views/controls/md_slider.h
diff --git a/ui/views/controls/md_slider.h b/ui/views/controls/md_slider.h
index d9ceeecf0ca3785f5792e88e933e70acd777d052..75c8fda96a292ddb0cf3de5a5bc5507f28743834 100644
--- a/ui/views/controls/md_slider.h
+++ b/ui/views/controls/md_slider.h
@@ -29,10 +29,20 @@ class VIEWS_EXPORT MdSlider : public Slider {
  protected:
   // ui::Slider:
   int GetThumbWidth() override;
+  void SetHighlighted(bool is_highlighted) override;
 
  private:
+  // gfx::AnimationDelegate:
+  void AnimationProgressed(const gfx::Animation* animation) override;
+  void AnimationEnded(const gfx::Animation* animation) override;
+
   // Record whether the slider is in the active state or the disabled state.
   bool is_active_;
+
+  // Animating value of the current radius size of the thumb's highlight.
+  float thumb_highlight_radius_;
+
+  std::unique_ptr<gfx::SlideAnimation> highlight_animation_;
 };
 
 }  // namespace views