Add ripple effect to new-style notification header.

ui/message_center/views/notification_header_view.h

Index: ui/message_center/views/notification_header_view.h
diff --git a/ui/message_center/views/notification_header_view.h b/ui/message_center/views/notification_header_view.h
index 640f6be47f62f4db7c77934f5f10517dbb2da419..addc8d195b7ef56831b0624d93f99208972d973e 100644
--- a/ui/message_center/views/notification_header_view.h
+++ b/ui/message_center/views/notification_header_view.h
@@ -34,6 +34,12 @@ class NotificationHeaderView : public views::CustomButton {
   bool IsCloseButtonEnabled();
   bool IsCloseButtonFocused();
 
+  // CustomButton override:
+  std::unique_ptr<views::InkDrop> CreateInkDrop() override;
+  std::unique_ptr<views::InkDropRipple> CreateInkDropRipple() const override;
+  std::unique_ptr<views::InkDropHighlight> CreateInkDropHighlight()
+      const override;
+
   views::ImageButton* expand_button() { return expand_button_; }
   views::ImageButton* settings_button() { return settings_button_; }
   views::ImageButton* close_button() { return close_button_; }