CrOS Shelf: Animate changes in the hotseat background's width

Bug: 1042491
Change-Id: I28e5d2ffb9a960e1146a8b6496ffd920e5d56509
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2035867Reviewed-by: Andrew Xu <andrewxu@chromium.org>
Commit-Queue: Manu Cornet <manucornet@chromium.org>
Cr-Commit-Position: refs/heads/master@{#737872}

ash/shelf/hotseat_widget.cc

@@ -173,15 +173,23 @@ void HotseatWidget::DelegateView::SetTranslucentBackground(
 
   translucent_background_.SetVisible(true);
 
+  // Animate the bounds change if we're changing the background, or if there's
+  // a change of width (for instance when dragging an app into, or out of,
+  // the shelf.
+  bool animate =
+      ShelfConfig::Get()->GetDefaultShelfColor() != target_color_ ||
+      background_bounds.width() != translucent_background_.bounds().width();
+  ui::ScopedLayerAnimationSettings animation_setter(
+      translucent_background_.GetAnimator());
+  animation_setter.SetTransitionDuration(
+      animate ? ShelfConfig::Get()->shelf_animation_duration()
+              : base::TimeDelta::FromMilliseconds(0));
+  animation_setter.SetTweenType(gfx::Tween::EASE_OUT);
+  animation_setter.SetPreemptionStrategy(
+      ui::LayerAnimator::IMMEDIATELY_ANIMATE_TO_NEW_TARGET);
+
   if (ShelfConfig::Get()->GetDefaultShelfColor() != target_color_) {
     target_color_ = ShelfConfig::Get()->GetDefaultShelfColor();
-    ui::ScopedLayerAnimationSettings animation_setter(
-        translucent_background_.GetAnimator());
-    animation_setter.SetTransitionDuration(
-        ShelfConfig::Get()->shelf_animation_duration());
-    animation_setter.SetTweenType(gfx::Tween::EASE_OUT);
-    animation_setter.SetPreemptionStrategy(
-        ui::LayerAnimator::IMMEDIATELY_ANIMATE_TO_NEW_TARGET);
     translucent_background_.SetColor(target_color_);
   }