Cros: Reland "Add metrics for transitions in the hotseat"

Report animation smoothness for the transition into the hotseat in the
HomeLauncher.

The original change caused use-of-uninitialized-value flaky tests. This
is a possible fix for the issue by explicitly resetting the
|animation_metrics_reporter_|

Bug: 1022178, 1022177, 1028255
Change-Id: I9abe9532e4f8b8cbc8c3700b21db48144f76f767
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1940562Reviewed-by: Manu Cornet <manucornet@chromium.org>
Commit-Queue: Ana Salazar <anasalazar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#720619}

ash/shelf/hotseat_transition_animator.cc

@@ -8,6 +8,7 @@
 #include "ash/shelf/shelf_widget.h"
 #include "ash/shell.h"
 #include "ash/wm/tablet_mode/tablet_mode_controller.h"
+#include "base/metrics/histogram_macros.h"
 #include "ui/compositor/layer.h"
 #include "ui/compositor/layer_animator.h"
 #include "ui/compositor/scoped_layer_animation_settings.h"
@@ -16,8 +17,37 @@
 
 namespace ash {
 
+class HotseatTransitionAnimator::TransitionAnimationMetricsReporter
+    : public ui::AnimationMetricsReporter {
+ public:
+  TransitionAnimationMetricsReporter() {}
+  ~TransitionAnimationMetricsReporter() override = default;
+  void animating_to_shown_hotseat(bool animating_to_shown_hotseat) {
+    animating_to_shown_hotseat_ = animating_to_shown_hotseat;
+  }
+  // ui::AnimationMetricsReporter:
+  void Report(int value) override {
+    if (animating_to_shown_hotseat_) {
+      UMA_HISTOGRAM_PERCENTAGE(
+          "Ash.HotseatTransition.AnimationSmoothness.TransitionToShownHotseat",
+          value);
+    } else {
+      UMA_HISTOGRAM_PERCENTAGE(
+          "Ash.HotseatTransition.AnimationSmoothness."
+          "TransitionFromShownHotseat",
+          value);
+    }
+  }
+
+ private:
+  // Whether the animation reported is transitioning state into a shown hotseat.
+  bool animating_to_shown_hotseat_ = false;
+};
+
 HotseatTransitionAnimator::HotseatTransitionAnimator(ShelfWidget* shelf_widget)
-    : shelf_widget_(shelf_widget) {
+    : shelf_widget_(shelf_widget),
+      animation_metrics_reporter_(
+          std::make_unique<TransitionAnimationMetricsReporter>()) {
   Shell::Get()->tablet_mode_controller()->AddObserver(this);
 }
 
@@ -25,6 +55,10 @@ HotseatTransitionAnimator::~HotseatTransitionAnimator() {
   StopObservingImplicitAnimations();
   if (Shell::Get()->tablet_mode_controller())
     Shell::Get()->tablet_mode_controller()->RemoveObserver(this);
+  // Reset the pointer for |animation_metrics_reporter| to delete the reference
+  // to the TransitionAnimationMetricsReporter object that might cause a
+  // use-of-uninitialized-value. (See crbug.com/1028255)
+  animation_metrics_reporter_.reset();
 }
 
 void HotseatTransitionAnimator::OnHotseatStateChanged(HotseatState old_state,
@@ -90,6 +124,8 @@ void HotseatTransitionAnimator::DoAnimation(HotseatState old_state,
   const int y_offset = starting_y - target_bounds.y();
   transform.Translate(0, y_offset);
   shelf_widget_->GetAnimatingBackground()->SetTransform(transform);
+  animation_metrics_reporter_->animating_to_shown_hotseat(
+      animating_to_shown_hotseat);
 
   {
     ui::ScopedLayerAnimationSettings shelf_bg_animation_setter(
@@ -99,6 +135,8 @@ void HotseatTransitionAnimator::DoAnimation(HotseatState old_state,
     shelf_bg_animation_setter.SetTweenType(gfx::Tween::EASE_OUT);
     shelf_bg_animation_setter.SetPreemptionStrategy(
         ui::LayerAnimator::IMMEDIATELY_ANIMATE_TO_NEW_TARGET);
+    shelf_bg_animation_setter.SetAnimationMetricsReporter(
+        animation_metrics_reporter_.get());
     animation_complete_callback_ = base::BindOnce(
         &HotseatTransitionAnimator::NotifyHotseatTransitionAnimationEnded,
         weak_ptr_factory_.GetWeakPtr(), old_state, new_state);

ash/shelf/hotseat_transition_animator.h

@@ -49,6 +49,8 @@ class HotseatTransitionAnimator : public TabletModeObserver,
   void OnTabletModeEnded() override;
 
  private:
+  class TransitionAnimationMetricsReporter;
+
   // Starts the animation between |old_state| and |target_state|.
   void DoAnimation(HotseatState old_state, HotseatState new_state);
 
@@ -71,6 +73,10 @@ class HotseatTransitionAnimator : public TabletModeObserver,
 
   base::ObserverList<Observer> observers_;
 
+  // Metric reporter for hotseat transitions.
+  std::unique_ptr<TransitionAnimationMetricsReporter>
+      animation_metrics_reporter_;
+
   base::WeakPtrFactory<HotseatTransitionAnimator> weak_ptr_factory_{this};
 };