CrOS Shelf: Show square highlights in the in-app shelf

Bug: 982511, 1009525
Change-Id: Iaa4b571c9ed8db5e0317f27096053c48ab5149a2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1832622Reviewed-by: Alex Newcomer <newcomer@chromium.org>
Commit-Queue: Alex Newcomer <newcomer@chromium.org>
Commit-Queue: Manu Cornet <manucornet@chromium.org>
Auto-Submit: Manu Cornet <manucornet@chromium.org>
Cr-Commit-Position: refs/heads/master@{#701322}

ash/shelf/shelf_config.cc

@@ -183,7 +183,9 @@ int ShelfConfig::control_size() const {
 }
 
 int ShelfConfig::control_border_radius() const {
-  return control_size() / 2;
+  return (is_in_app() && Shell::Get()->tablet_mode_controller()->InTabletMode())
+             ? 0
+             : control_size() / 2;
 }
 
 int ShelfConfig::overflow_button_margin() const {