Add tablet mode check for IsHomeScreenVisible.

Bug: 1002733
Change-Id: I97b7ba270f2df51c0a433d3ba0320e33ef3dc94b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1861019Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Min Chen <minch@chromium.org>
Cr-Commit-Position: refs/heads/master@{#705992}

ash/app_list/app_list_controller_impl.cc

@@ -1501,7 +1501,7 @@ void AppListControllerImpl::NotifyHomeLauncherAnimationTransition(
 }
 
 bool AppListControllerImpl::IsHomeScreenVisible() {
-  return IsVisible();
+  return IsTabletMode() && IsVisible();
 }
 
 }  // namespace ash