cros: Add layers to bring the launcher open/close animation back

This animation was removed unintentionally, this CL brings it back.
Also added better comments so the animation's importance is more
obvious.

Bug: 910496
Change-Id: If505bea1683d7ae456dcedbdb0a9e97ea58e02de
Reviewed-on: https://chromium-review.googlesource.com/c/1368604Reviewed-by: Jenny Zhang <jennyz@chromium.org>
Reviewed-by: Mitsuru Oshima (gardener - slow) <oshima@chromium.org>
Commit-Queue: Alex Newcomer <newcomer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#616080}

ash/app_list/presenter/app_list_presenter_impl.cc

@@ -311,8 +311,9 @@ void AppListPresenterImpl::ScheduleAnimation() {
   aura::Window* root_window = widget->GetNativeView()->GetRootWindow();
   const gfx::Vector2d offset =
       delegate_->GetVisibilityAnimationOffset(root_window);
-  base::TimeDelta animation_duration =
-      delegate_->GetVisibilityAnimationDuration(root_window, is_visible_);
+  const base::TimeDelta animation_duration =
+      delegate_->GetVisibilityAnimationDuration(root_window,
+                                                view_->is_fullscreen());
   gfx::Rect target_bounds = widget->GetNativeView()->bounds();
   target_bounds.Offset(offset);
   widget->GetNativeView()->SetBounds(target_bounds);

ash/app_list/views/app_list_main_view.cc

@@ -74,6 +74,8 @@ void AppListMainView::AddContentsViews() {
   DCHECK(search_box_view_);
   contents_view_ = new ContentsView(app_list_view_);
   contents_view_->Init(model_);
+  contents_view_->SetPaintToLayer(ui::LAYER_NOT_DRAWN);
+  contents_view_->layer()->SetMasksToBounds(true);
   AddChildView(contents_view_);
 
   search_box_view_->set_contents_view(contents_view_);

ash/app_list/views/app_list_view.cc

@@ -1231,6 +1231,15 @@ void AppListView::StartAnimationForState(AppListViewState target_state) {
     animation_duration = kAppListAnimationDurationMs;
   }
 
+  if (fullscreen_widget_->GetNativeView()->bounds().y() ==
+      display.work_area().bottom()) {
+    // If the animation start position is the bottom of the screen, activate the
+    // fade in animation. This prevents the search box from flashing at the
+    // bottom of the screen as it goes behind the shelf.
+    app_list_main_view_->contents_view()->FadeInOnOpen(
+        base::TimeDelta::FromMilliseconds(animation_duration));
+  }
+
   ui::Layer* layer = fullscreen_widget_->GetLayer();
   layer->SetBounds(target_bounds);
   gfx::Transform transform;
@@ -1260,7 +1269,15 @@ void AppListView::StartCloseAnimation(base::TimeDelta animation_duration) {
   if (is_side_shelf_)
     return;
 
+  // If animating from PEEKING, animate the opacity twice as fast so the
+  // SearchBoxView does not flash behind the shelf.
+  if (app_list_state_ == AppListViewState::PEEKING ||
+      app_list_state_ == AppListViewState::CLOSED) {
+    animation_duration /= 2;
+  }
+
   SetState(AppListViewState::CLOSED);
+  app_list_main_view_->contents_view()->FadeOutOnClose(animation_duration);
 }
 
 void AppListView::SetStateFromSearchBoxView(bool search_box_is_empty,

ash/app_list/views/contents_view.cc

@@ -42,6 +42,17 @@ namespace {
 constexpr float kExpandArrowOpacityStartProgress = 0.61;
 constexpr float kExpandArrowOpacityEndProgress = 1;
 
+void DoAnimation(base::TimeDelta animation_duration,
+                 ui::Layer* layer,
+                 float target_opacity) {
+  ui::ScopedLayerAnimationSettings animation(layer->GetAnimator());
+  animation.SetTransitionDuration(animation_duration);
+  animation.SetTweenType(gfx::Tween::EASE_IN);
+  animation.SetPreemptionStrategy(
+      ui::LayerAnimator::IMMEDIATELY_ANIMATE_TO_NEW_TARGET);
+  layer->SetOpacity(target_opacity);
+}
+
 }  // namespace
 
 ContentsView::ContentsView(AppListView* app_list_view)
@@ -507,6 +518,18 @@ void ContentsView::TransitionChanged() {
 
 void ContentsView::TransitionEnded() {}
 
+void ContentsView::FadeOutOnClose(base::TimeDelta animation_duration) {
+  DoAnimation(animation_duration, layer(), 0.0f);
+  DoAnimation(animation_duration, GetSearchBoxView()->layer(), 0.0f);
+}
+
+void ContentsView::FadeInOnOpen(base::TimeDelta animation_duration) {
+  GetSearchBoxView()->layer()->SetOpacity(0.0f);
+  layer()->SetOpacity(0.0f);
+  DoAnimation(animation_duration, layer(), 1.0f);
+  DoAnimation(animation_duration, GetSearchBoxView()->layer(), 1.0f);
+}
+
 views::View* ContentsView::GetSelectedView() const {
   return app_list_pages_[GetActivePageIndex()]->GetSelectedView();
 }

ash/app_list/views/contents_view.h

@@ -150,6 +150,14 @@ class APP_LIST_EXPORT ContentsView : public views::View,
   void Layout() override;
   const char* GetClassName() const override;
 
+  // Starts the fade out animation when the app list is closed. This
+  // prevents the contents from being visible behind the shelf.
+  void FadeOutOnClose(base::TimeDelta animation_duration);
+
+  // Starts the fade in animation when the app list is opened. This prevents the
+  // contents from being visible behind the shelf.
+  void FadeInOnOpen(base::TimeDelta animation_duration);
+
   // Overridden from PaginationModelObserver:
   void TotalPagesChanged() override;
   void SelectedPageChanged(int old_selected, int new_selected) override;