Fix previews on shelf alignment/config change.

Addresses two issues:
1. When shelf alignment/config changed any previews that were in the
   process of being removed were appropriately destroyed. However, we
   failed to call `OnOldItemsRemoved()` after so any new/existing items
   weren't animated/shifted into position. The result was missing and
   misplaced previews.
2. The translation calculation in `OnShelfConfigChanged()` was slightly
   off. Fixed with index based calculation.

Bug: 1166804
Change-Id: Ifda6a6a4fa527bfc6753840a7257fc92c9446a20
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2631293Reviewed-by: Toni Baržić <tbarzic@chromium.org>
Reviewed-by: David Black <dmblack@google.com>
Commit-Queue: David Black <dmblack@google.com>
Cr-Commit-Position: refs/heads/master@{#843890}

ash/system/holding_space/holding_space_tray_icon.cc

@@ -239,7 +239,11 @@ void HoldingSpaceTrayIcon::UpdatePreviews(
 void HoldingSpaceTrayIcon::OnShelfAlignmentChanged(
     aura::Window* root_window,
     ShelfAlignment old_alignment) {
-  removed_previews_.clear();
+  if (!removed_previews_.empty()) {
+    removed_previews_.clear();
+    OnOldItemsRemoved();
+  }
+
   for (const auto& preview : previews_by_id_)
     preview.second->OnShelfAlignmentChanged(old_alignment, shelf_->alignment());
 
@@ -253,7 +257,11 @@ void HoldingSpaceTrayIcon::OnShelfAlignmentChanged(
 }
 
 void HoldingSpaceTrayIcon::OnShelfConfigUpdated() {
-  removed_previews_.clear();
+  if (!removed_previews_.empty()) {
+    removed_previews_.clear();
+    OnOldItemsRemoved();
+  }
+
   for (const auto& preview : previews_by_id_)
     preview.second->OnShelfConfigChanged();
 

ash/system/holding_space/holding_space_tray_icon_preview.cc

@@ -366,9 +366,9 @@ void HoldingSpaceTrayIconPreview::OnShelfConfigChanged() {
     return;
 
   // Adjust `translation` to account for the change in size.
-  gfx::Vector2dF translation = transform_.To2dTranslation();
-  translation.Scale(1.f / GetPreviewSize(!use_small_previews_).width());
-  translation.Scale(GetPreviewSize().width());
+  DCHECK(index_);
+  gfx::Vector2dF translation(*index_ * GetPreviewSize().width() / 2, 0);
+  AdjustForShelfAlignmentAndTextDirection(&translation);
   transform_.MakeIdentity();
   transform_.Translate(translation);