Adding ripple effect for clicks on MD slider

ui/views/controls/md_slider.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_VIEWS_CONTROLS_MD_SLIDER_H_
 #define UI_VIEWS_CONTROLS_MD_SLIDER_H_
 
 #include "base/macros.h"
 #include "ui/views/controls/slider.h"
 #include "ui/views/view.h"
@@ skipping 13 matching lines @@
 
   // views::View:
   void OnPaint(gfx::Canvas* canvas) override;
   const char* GetClassName() const override;
 
  protected:
   // ui::Slider:
   int GetThumbWidth() override;
 
  private:
+  // views::View:
+  bool OnMousePressed(const ui::MouseEvent& event) override;

[bruthig, 2016/09/12 17:16:48]

What about touch and keyboard interactions?  I assume we would want the
highlight for touch for sure but don't know about keyboard.

It might make sense to re-use the Slider::PrepareForMove() method as
MousePressed() and OnGestureEvent() already call this.

[yiyix, 2016/09/20 20:25:46]

Instead of override functions, I created a new function called SetFocus, which
will be set when the slider is selected. Please take a look at this new
approach.

+  void OnMouseReleased(const ui::MouseEvent& event) override;
+
   // Record whether the slider is in the active state or the disabled state.
   bool is_active_;
+
+  // It is true if there is a press event or a touch event in this view
+  // currently; otherwise, it is false.
+  bool is_pressed_;
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_CONTROLS_MD_SLIDER_H_