desks: Remove vector of desk animations in DesksController.

Both creaters of desk animations have a guard to stop creation of a new
animation. For enhanced desk animations, we will append to an existing
animation, so a vector is not needed anymore.

Test: manual
Bug: 1111445
Change-Id: Ic615e73cc28ac9bb1e7746782a1455c90e11a2a7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2412687Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#807308}

ash/wm/desks/desks_controller.cc

@@ -163,13 +163,13 @@ DesksController* DesksController::Get() {
 }
 
 const Desk* DesksController::GetTargetActiveDesk() const {
-  if (!animations_.empty())
-    return desks_[animations_.back()->ending_desk_index()].get();
+  if (animation_)
+    return desks_[animation_->ending_desk_index()].get();
   return active_desk();
 }
 
 void DesksController::Shutdown() {
-  animations_.clear();
+  animation_.reset();
 }
 
 void DesksController::AddObserver(Observer* observer) {
@@ -181,7 +181,7 @@ void DesksController::RemoveObserver(Observer* observer) {
 }
 
 bool DesksController::AreDesksBeingModified() const {
-  return are_desks_being_modified_ || !animations_.empty();
+  return are_desks_being_modified_ || !!animation_;
 }
 
 bool DesksController::CanCreateDesks() const {
@@ -256,9 +256,9 @@ void DesksController::RemoveDesk(const Desk* desk,
         current_desk_index + ((current_desk_index > 0) ? -1 : 1);
     DCHECK_GE(target_desk_index, 0);
     DCHECK_LT(target_desk_index, static_cast<int>(desks_.size()));
-    animations_.emplace_back(std::make_unique<DeskRemovalAnimation>(
-        this, current_desk_index, target_desk_index, source));
-    animations_.back()->Launch();
+    animation_ = std::make_unique<DeskRemovalAnimation>(
+        this, current_desk_index, target_desk_index, source);
+    animation_->Launch();
     return;
   }
 
@@ -267,7 +267,7 @@ void DesksController::RemoveDesk(const Desk* desk,
 
 void DesksController::ActivateDesk(const Desk* desk, DesksSwitchSource source) {
   DCHECK(HasDesk(desk));
-  DCHECK(animations_.empty());
+  DCHECK(!animation_);
 
   OverviewController* overview_controller = Shell::Get()->overview_controller();
   const bool in_overview = overview_controller->InOverviewSession();
@@ -300,9 +300,9 @@ void DesksController::ActivateDesk(const Desk* desk, DesksSwitchSource source) {
   }
 
   const int starting_desk_index = GetDeskIndex(active_desk());
-  animations_.emplace_back(std::make_unique<DeskActivationAnimation>(
-      this, starting_desk_index, target_desk_index, source));
-  animations_.back()->Launch();
+  animation_ = std::make_unique<DeskActivationAnimation>(
+      this, starting_desk_index, target_desk_index, source);
+  animation_->Launch();
 }
 
 bool DesksController::ActivateAdjacentDesk(bool going_left,
@@ -316,15 +316,9 @@ bool DesksController::ActivateAdjacentDesk(bool going_left,
     return false;
 
   // Try replacing an ongoing desk animation of the same source.
-  if (is_enhanced_desk_animations_) {
-    for (const auto& animation : animations_) {
-      if (animation->Replace(going_left, source))
-        return true;
-    }
-    // If there is no current animation of the same source but there is an
-    // animation running, skip this animation.
-    if (!animations_.empty())
-      return false;
+  if (is_enhanced_desk_animations_ && animation_ &&
+      animation_->Replace(going_left, source)) {
+    return true;
   }
 
   const Desk* desk_to_activate = going_left ? GetPreviousDesk() : GetNextDesk();
@@ -349,18 +343,14 @@ bool DesksController::StartAnimationForGesture(bool move_left) {
 
 void DesksController::UpdateAnimationForGesture(float scroll_delta_x) {
   DCHECK(is_enhanced_desk_animations_);
-  for (const auto& animation : animations_) {
-    if (animation->Update(scroll_delta_x))
-      return;
-  }
+  if (animation_)
+    animation_->Update(scroll_delta_x);
 }
 
 void DesksController::EndAnimationForGesture() {
   DCHECK(is_enhanced_desk_animations_);
-  for (const auto& animation : animations_) {
-    if (animation->End())
-      return;
-  }
+  if (animation_)
+    animation_->End();
 }
 
 bool DesksController::MoveWindowFromActiveDeskTo(
@@ -503,7 +493,8 @@ void DesksController::OnFirstSessionStarted() {
 }
 
 void DesksController::OnAnimationFinished(DeskAnimationBase* animation) {
-  base::EraseIf(animations_, base::MatchesUniquePtr(animation));
+  DCHECK_EQ(animation_.get(), animation);
+  animation_.reset();
 }
 
 bool DesksController::HasDesk(const Desk* desk) const {

ash/wm/desks/desks_controller.h

@@ -230,9 +230,8 @@ class ASH_EXPORT DesksController : public DesksHelper,
   // mode as a result of desks modifications.
   bool are_desks_being_modified_ = false;
 
-  // List of on-going desks animations.
-  // TODO(sammiequon): Investigate if this needs to still be a list.
-  std::vector<std::unique_ptr<DeskAnimationBase>> animations_;
+  // Not null if there is an on-going desks animation.
+  std::unique_ptr<DeskAnimationBase> animation_;
 
   // A free list of desk container IDs to be used for newly-created desks. New
   // desks pops from this queue and removed desks's associated container IDs are