desks: Ensure OnDeskSwitchAnimation Launching/Finished are paired up.

Moves Finished to the destructor so it is always paired up with a
Launching. Shelf relies on the two being paired up so it is hidden and
shown properly.

It's possible to modify Replace to have more return codes and handle the
case a screenshot is not yet taken more gracefully. However, if a new
use of Replace is added the user will have to ensure a new animation is
not created on top of an existing one.

Bug: 1166475
Test: manual
Change-Id: I9d1ca10d4a028ee881af821ee4063ed2576c3b35
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2633069
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#844245}

ash/wm/desks/desk_animation_base.cc

@@ -27,7 +27,10 @@ DeskAnimationBase::DeskAnimationBase(DesksController* controller,
   DCHECK_GE(ending_desk_index_, 0);
 }
 
-DeskAnimationBase::~DeskAnimationBase() = default;
+DeskAnimationBase::~DeskAnimationBase() {
+  for (auto& observer : controller_->observers_)
+    observer.OnDeskSwitchAnimationFinished();
+}
 
 void DeskAnimationBase::Launch() {
   for (auto& observer : controller_->observers_)
@@ -128,9 +131,6 @@ void DeskAnimationBase::OnDeskSwitchAnimationFinished() {
 
   throughput_tracker_.Stop();
 
-  for (auto& observer : controller_->observers_)
-    observer.OnDeskSwitchAnimationFinished();
-
   if (skip_notify_controller_on_animation_finished_for_testing_)
     return;