Disable ink drop effect for arrow button

As requested by UX team, disable the ink drop effect of the scrollable
shelf's arrow button by this CL.

Bug: 1019012
Change-Id: I6a7224911cafb70167d4f152b53b93fdd3fa6004
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1885500
Auto-Submit: Andrew Xu <andrewxu@chromium.org>
Commit-Queue: Manu Cornet <manucornet@chromium.org>
Reviewed-by: Manu Cornet <manucornet@chromium.org>
Cr-Commit-Position: refs/heads/master@{#710339}

ash/shelf/scrollable_shelf_view.cc

@@ -192,6 +192,7 @@ class ScrollableShelfView::ScrollableShelfArrowView
                         is_horizontal_alignment,
                         shelf,
                         shelf_button_delegate) {
+    SetInkDropMode(InkDropMode::OFF);
     SetEventTargeter(std::make_unique<views::ViewTargeter>(this));
   }
   ~ScrollableShelfArrowView() override = default;