Adds trace event for launcher state transition animation.

Bug: 961467
Test: manually seeing chrome://tracing
Change-Id: I0303adeea2ba52f656811ab891ed6f0a7bcfbe65
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1604050Reviewed-by: Alex Newcomer <newcomer@chromium.org>
Commit-Queue: Jun Mukai <mukai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#658391}

ash/app_list/presenter/app_list_presenter_impl.cc

@@ -379,6 +379,7 @@ void AppListPresenterImpl::ScheduleDismissAnimation() {
     animation.SetAnimationMetricsReporter(
         view_->GetStateTransitionMetricsReporter());
     animation.AddObserver(this);
+    TRACE_EVENT_ASYNC_BEGIN0("ui", "AppList::StateTransitionAnimations", this);
 
     layer->SetTransform(gfx::Transform());
   }
@@ -446,6 +447,9 @@ void AppListPresenterImpl::OnWindowFocused(aura::Window* gained_focus,
 // AppListPresenterImpl, ui::ImplicitAnimationObserver implementation:
 
 void AppListPresenterImpl::OnImplicitAnimationsCompleted() {
+  // This class observes the closing animation only.
+  TRACE_EVENT_ASYNC_END1("ui", "AppList::StateTransitionAnimations", this,
+                         "state", ash::mojom::AppListViewState::kClosed);
   NotifyVisibilityChanged(GetTargetVisibility(), GetDisplayId());
 
   if (is_visible_) {

ash/app_list/views/app_list_view.cc

@@ -386,6 +386,8 @@ class TransitionAnimationObserver : public ui::ImplicitAnimationObserver {
 
   // ui::ImplicitAnimationObserver:
   void OnImplicitAnimationsCompleted() override {
+    TRACE_EVENT_ASYNC_END1("ui", "AppList::StateTransitionAnimations", this,
+                           "state", view_->app_list_state());
     DCHECK(view_);
     view_->Layout();
   }
@@ -1544,6 +1546,8 @@ void AppListView::StartAnimationForState(
 
   settings.SetAnimationMetricsReporter(GetStateTransitionMetricsReporter());
   settings.AddObserver(transition_animation_observer_.get());
+  TRACE_EVENT_ASYNC_BEGIN0("ui", "AppList::StateTransitionAnimations",
+                           transition_animation_observer_.get());
 
   layer->SetTransform(gfx::Transform());