Fix HoldingSpaceTrayIcon size.

Currently HoldingSpaceTrayIcon is updating preferred size when shelf
alignment changes. This is desired behavior when the content forward
entry point is enabled, but this is *not* desired behavior when the
content forward entry point is disabled.

Bug: 1142572
Change-Id: I6ae728cf9968af87934d694a51b293ae64e7e8ed
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2520380Reviewed-by: Toni Baržić <tbarzic@chromium.org>
Commit-Queue: David Black <dmblack@google.com>
Cr-Commit-Position: refs/heads/master@{#824312}

ash/system/holding_space/holding_space_tray_icon.cc

@@ -25,10 +25,10 @@ namespace ash {
 HoldingSpaceTrayIcon::HoldingSpaceTrayIcon(Shelf* shelf) : shelf_(shelf) {
   InitLayout();
 
-  if (features::IsTemporaryHoldingSpaceContentForwardEntryPointEnabled())
+  if (features::IsTemporaryHoldingSpaceContentForwardEntryPointEnabled()) {
     controller_observer_.Add(HoldingSpaceController::Get());
-
-  shell_observer_.Add(Shell::Get());
+    shell_observer_.Add(Shell::Get());
+  }
 }
 
 HoldingSpaceTrayIcon::~HoldingSpaceTrayIcon() = default;
@@ -142,6 +142,8 @@ void HoldingSpaceTrayIcon::OnHoldingSpaceItemFinalized(
 void HoldingSpaceTrayIcon::OnShelfAlignmentChanged(
     aura::Window* root_window,
     ShelfAlignment old_alignment) {
+  DCHECK(features::IsTemporaryHoldingSpaceContentForwardEntryPointEnabled());
+
   removed_icon_items_.clear();
 
   for (const auto& icon_item : icon_items_)