Fix the issue of wrong layout after tablet-clamshell transition

This bug was introduced by my previous CL (https://crrev.com/c/1811183).
In that CL, calculating the edge padding was put before the update of
layout strategy. In this CL, replacing the check on layout strategy with
calling CanFitAllAppsWithoutScrolling.

Bug: 1006379
Change-Id: I74b6e0f85662d1c5c31cdbe0d1139357000a3321
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1828060Reviewed-by: Manu Cornet <manucornet@chromium.org>
Commit-Queue: Andrew Xu <andrewxu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#700413}

ash/shelf/scrollable_shelf_view.cc

@@ -715,7 +715,7 @@ gfx::Insets ScrollableShelfView::CalculateEdgePadding() const {
       2 * ShelfConfig::Get()->app_icon_group_margin();
 
   int gap =
-      layout_strategy_ == kNotShowArrowButtons
+      CanFitAllAppsWithoutScrolling()
           ? available_size_for_app_icons - icons_size  // shelf centering
           : CalculateOverflowPadding(available_size_for_app_icons);  // overflow