Adds entry/exit animations for in-Assistant notifications.

Per UX requirements, in-Assistant notifications should be animated in
and out smoothly.

Demo:
https://drive.google.com/open?id=1KPaOCen6pmHFV8_SRV1w5hqYNDBN2xsJ

Bug: b:118654460
Change-Id: Ie02827f8a0d864cd2f652b668b9880bcd51246df
Reviewed-on: https://chromium-review.googlesource.com/c/1483708
Commit-Queue: David Black <dmblack@google.com>
Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#636138}

ash/assistant/ui/assistant_notification_view.cc

@@ -9,6 +9,7 @@
 #include "ash/assistant/ui/main_stage/suggestion_chip_view.h"
 #include "base/strings/utf_string_conversions.h"
 #include "chromeos/services/assistant/public/mojom/assistant.mojom.h"
+#include "ui/compositor/scoped_layer_animation_settings.h"
 #include "ui/views/animation/ink_drop_painted_layer_delegates.h"
 #include "ui/views/controls/button/button.h"
 #include "ui/views/controls/label.h"
@@ -26,6 +27,10 @@ constexpr int kPaddingRightDip = 8;
 constexpr int kPreferredHeightDip = 48;
 constexpr int kShadowElevationDip = 6;
 
+// Animation.
+constexpr base::TimeDelta kAnimationDuration =
+    base::TimeDelta::FromMilliseconds(250);
+
 // Helpers ---------------------------------------------------------------------
 
 views::View* CreateButton(
@@ -56,6 +61,10 @@ const char* AssistantNotificationView::GetClassName() const {
   return "AssistantNotificationView";
 }
 
+void AssistantNotificationView::AddedToWidget() {
+  UpdateVisibility(/*visible=*/true);
+}
+
 gfx::Size AssistantNotificationView::CalculatePreferredSize() const {
   return gfx::Size(INT_MAX, GetHeightForWidth(INT_MAX));
 }
@@ -77,6 +86,14 @@ void AssistantNotificationView::ButtonPressed(views::Button* sender,
                                          notification_button_index);
 }
 
+void AssistantNotificationView::OnImplicitAnimationsCompleted() {
+  // When the view's layer has animated to |0.f| opacity, the underlying
+  // notification has been removed and our associated view can be deleted. Note
+  // that we check for opacity within epsilon to avoid exact float comparison.
+  if (cc::MathUtil::IsWithinEpsilon(layer()->opacity(), 0.f))
+    delete this;
+}
+
 void AssistantNotificationView::OnNotificationUpdated(
     const AssistantNotification* notification) {
   // We only care about the |notification| being updated if it is the
@@ -90,7 +107,7 @@ void AssistantNotificationView::OnNotificationUpdated(
   // If the notification associated with this view is no longer of type
   // |kInAssistant|, it should not be shown in Assistant UI.
   if (notification->type != AssistantNotificationType::kInAssistant) {
-    delete this;
+    UpdateVisibility(/*visible=*/false);
     return;
   }
 
@@ -120,7 +137,7 @@ void AssistantNotificationView::OnNotificationRemoved(
     const AssistantNotification* notification,
     bool from_server) {
   if (notification->client_id == notification_id_)
-    delete this;
+    UpdateVisibility(/*visible=*/false);
 }
 
 void AssistantNotificationView::InitLayout(
@@ -130,6 +147,10 @@ void AssistantNotificationView::InitLayout(
   SetPaintToLayer();
   layer()->SetFillsBoundsOpaquely(false);
 
+  // Initialize opacity to |0.f| as the layer for this view will be animated in
+  // when the view is added to its widget.
+  layer()->SetOpacity(0.f);
+
   // Background/shadow.
   background_layer_.SetFillsBoundsOpaquely(false);
   layer()->Add(&background_layer_);
@@ -194,4 +215,22 @@ void AssistantNotificationView::UpdateBackground() {
       gfx::ToEnclosingRect(shadow_delegate_->GetPaintedBounds()));
 }
 
+void AssistantNotificationView::UpdateVisibility(bool visible) {
+  ui::ScopedLayerAnimationSettings animation(layer()->GetAnimator());
+
+  // We observe the animation to receive an event on its completion. When the
+  // layer for this view has completed animating to a hidden state, this view
+  // is deleted as the underlying notification has been removed.
+  animation.AddObserver(this);
+
+  // Parameters.
+  animation.SetPreemptionStrategy(
+      ui::LayerAnimator::PreemptionStrategy::IMMEDIATELY_ANIMATE_TO_NEW_TARGET);
+  animation.SetTransitionDuration(kAnimationDuration);
+  animation.SetTweenType(gfx::Tween::Type::EASE_IN_OUT);
+
+  // Animate opacity to a visible/hidden state.
+  layer()->SetOpacity(visible ? 1.f : 0.f);
+}
+
 }  // namespace ash

ash/assistant/ui/assistant_notification_view.h

@@ -13,6 +13,7 @@
 #include "base/component_export.h"
 #include "base/macros.h"
 #include "ui/compositor/layer.h"
+#include "ui/compositor/layer_animation_observer.h"
 #include "ui/views/controls/button/button.h"
 #include "ui/views/view.h"
 
@@ -30,6 +31,7 @@ class AssistantViewDelegate;
 class COMPONENT_EXPORT(ASSISTANT_UI) AssistantNotificationView
     : public views::View,
       public views::ButtonListener,
+      public ui::ImplicitAnimationObserver,
       public AssistantNotificationModelObserver {
  public:
   AssistantNotificationView(AssistantViewDelegate* delegate,
@@ -38,13 +40,17 @@ class COMPONENT_EXPORT(ASSISTANT_UI) AssistantNotificationView
 
   // views::View:
   const char* GetClassName() const override;
+  void AddedToWidget() override;
   gfx::Size CalculatePreferredSize() const override;
   int GetHeightForWidth(int width) const override;
   void OnBoundsChanged(const gfx::Rect& previous_bounds) override;
 
-  // views::Button:
+  // views::ButtonListener:
   void ButtonPressed(views::Button* sender, const ui::Event& event) override;
 
+  // ui::ImplicitAnimationObserver:
+  void OnImplicitAnimationsCompleted() override;
+
   // AssistantNotificationModelObserver:
   void OnNotificationUpdated(
       const AssistantNotification* notification) override;
@@ -54,6 +60,7 @@ class COMPONENT_EXPORT(ASSISTANT_UI) AssistantNotificationView
  private:
   void InitLayout(const AssistantNotification* notification);
   void UpdateBackground();
+  void UpdateVisibility(bool visible);
 
   AssistantViewDelegate* const delegate_;  // Owned by AssistantController.
   const std::string notification_id_;