cros: Remove launcher notch in tablet mode if gestures are disabled

The home launcher notch is shown normally to indicate that the launcher
can be dragged. This draggability is behind the HomeLauncherGestures
flag.

If this flag is disabled and the device is in tablet mode, do not draw
the notch.

Bug: 878937
Change-Id: I17b60cc689f39658edcb22bfb55be7ad53b26e34
Reviewed-on: https://chromium-review.googlesource.com/1195935
Commit-Queue: Weidong Guo <weidongg@chromium.org>
Reviewed-by: Weidong Guo <weidongg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#587649}

ash/app_list/views/contents_view.cc

@@ -314,6 +314,14 @@ void ContentsView::UpdateExpandArrowOpacity(double progress,
   if (!expand_arrow_view_)
     return;
 
+  // Don't show |expand_arrow_view_| when the home launcher gestures are
+  // disabled in tablet mode.
+  if (app_list_view_->IsHomeLauncherEnabledInTabletMode() &&
+      !features::IsHomeLauncherGesturesEnabled()) {
+    expand_arrow_view_->layer()->SetOpacity(0);
+    return;
+  }
+
   if (current_state == ash::AppListState::kStateSearchResults &&
       (target_state == ash::AppListState::kStateStart ||
        target_state == ash::AppListState::kStateApps)) {