Add MD ink drop ripple to shelf app items

ash/shelf/shelf_button.h

Index: ash/shelf/shelf_button.h
diff --git a/ash/shelf/shelf_button.h b/ash/shelf/shelf_button.h
index 4a84a61a532d502bb5d7a60e0047ef4beea274a6..e6085d279a4b0a4df7fe6635e781b02ed67c4a4d 100644
--- a/ash/shelf/shelf_button.h
+++ b/ash/shelf/shelf_button.h
@@ -54,6 +54,9 @@ class ASH_EXPORT ShelfButton : public views::CustomButton {
   // Returns the bounds of the icon.
   gfx::Rect GetIconBounds() const;
 
+  // Called when user started dragging the shelf button.
+  void OnDragStarted();
+
   // Overrides to views::CustomButton:
   void ShowContextMenu(const gfx::Point& p,
                        ui::MenuSourceType source_type) override;
@@ -77,6 +80,12 @@ class ASH_EXPORT ShelfButton : public views::CustomButton {
   // ui::EventHandler overrides:
   void OnGestureEvent(ui::GestureEvent* event) override;
 
+  // views::CustomButton overrides:
+  std::unique_ptr<views::InkDropRipple> CreateInkDropRipple() const override;
+  bool ShouldEnterPushedState(const ui::Event& event) override;
+  bool ShouldShowInkDropHighlight() const override;
+  void NotifyClick(const ui::Event& event) override;
+
   // Sets the icon image with a shadow.
   void SetShadowedImage(const gfx::ImageSkia& bitmap);