Fix double app icon when dragging app to shelf

When an app is being dragged from app list to shelf,
a new shelf item is created and made hidden by setting
its size to (0,0). It is supposed to stay at this size
until the drag is complete.

However, if a drag started very soon after some other shelf
manipulation (e.g. drag leaving the shelf and re-entering quickly),
it is possible for AnimateToIdealBounds to be called asynchronously.
The hidden item's bounds will be animated to full size, resulting
in a visible icon.

This CL makes AnimateToIdealBounds ignore shelf items with (0,0) size.

Bug: 985631
Test: manual
Change-Id: Ieb23beb6ecf635ae60613f5f6217219f7963999b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1862507
Commit-Queue: Vladislav Kaznacheev <kaznacheev@chromium.org>
Reviewed-by: Manu Cornet <manucornet@chromium.org>
Auto-Submit: Vladislav Kaznacheev <kaznacheev@chromium.org>
Cr-Commit-Position: refs/heads/master@{#706148}

ash/shelf/shelf_view.cc

@@ -1521,6 +1521,8 @@ void ShelfView::AnimateToIdealBounds() {
 
   for (int i = 0; i < view_model_->view_size(); ++i) {
     View* view = view_model_->view_at(i);
+    if (view->size() == gfx::Size())
+      continue;  // Do not animate a hidden item (see StartDrag)
     bounds_animator_->AnimateViewTo(view, view_model_->ideal_bounds(i));
     // Now that the item animation starts, we have to make sure that the
     // padding of the first gets properly transferred to the new first item.