CrOS Shelf: Correctly set shelf animating background color

Bug: 1032420
Change-Id: I034c96aa57f7818253ba96a7547d6481ec48e6a5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1959767Reviewed-by: Manu Cornet <manucornet@chromium.org>
Commit-Queue: Matthew Mourgos <mmourgos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#723664}

ash/shelf/hotseat_transition_animator.cc

@@ -99,6 +99,9 @@ void HotseatTransitionAnimator::DoAnimation(HotseatState old_state,
 
   const bool animating_to_shown_hotseat = new_state == HotseatState::kShown;
 
+  shelf_widget_->GetAnimatingBackground()->SetColor(
+      ShelfConfig::Get()->GetMaximizedShelfColor());
+
   gfx::Rect target_bounds = shelf_widget_->GetOpaqueBackground()->bounds();
   target_bounds.set_height(ShelfConfig::Get()->in_app_shelf_size());
   target_bounds.set_y(