desks: Shift desks items when swiping to close overview.

Test: manual
Bug: 1005354
Change-Id: I5674ed65831e640ddb17012ac41eb7e694f975f9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1818716
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#699537}

ash/wm/overview/overview_grid.cc

@@ -1186,14 +1186,25 @@ OverviewGrid::UpdateYPositionAndOpacity(
     int new_y,
     float opacity,
     OverviewSession::UpdateAnimationSettingsCallback callback) {
-  DCHECK(!window_list_.empty());
-  // Translate the window items to |new_y| with the opacity. Observe the
-  // animation of the first window.
   std::unique_ptr<ui::ScopedLayerAnimationSettings> settings_to_observe;
+  if (desks_widget_) {
+    aura::Window* window = desks_widget_->GetNativeWindow();
+    ui::Layer* layer = window->layer();
+    if (!callback.is_null()) {
+      settings_to_observe = std::make_unique<ui::ScopedLayerAnimationSettings>(
+          layer->GetAnimator());
+      callback.Run(settings_to_observe.get());
+    }
+    window->SetTransform(gfx::Transform(1.f, 0.f, 0.f, 1.f, 0.f, -new_y));
+    layer->SetOpacity(opacity);
+  }
+
+  // Translate the window items to |new_y| with the opacity. Observe the
+  // animation of the last item, if any.
   for (const auto& window_item : window_list_) {
     auto new_settings =
         window_item->UpdateYPositionAndOpacity(new_y, opacity, callback);
-    if (!settings_to_observe && new_settings)
+    if (new_settings)
       settings_to_observe = std::move(new_settings);
   }
   return settings_to_observe;

ash/wm/overview/overview_grid.h

@@ -227,6 +227,7 @@ class ASH_EXPORT OverviewGrid : public ScreenRotationAnimatorObserver,
   // transformation and opacity change should be animated. The animation
   // settings will be set by the caller via |callback|. Returns the settings of
   // the first window we are animating; the caller will observe this animation.
+  // The returned object may be nullptr.
   std::unique_ptr<ui::ScopedLayerAnimationSettings> UpdateYPositionAndOpacity(
       int new_y,
       float opacity,

ash/wm/overview/overview_item.cc

@@ -315,12 +315,10 @@ OverviewItem::UpdateYPositionAndOpacity(
     // Alter the y-translation. Offset by the window location relative to the
     // grid.
     gfx::Transform transform = layer->transform();
-    transform.matrix().setFloat(1, 3,
-                                static_cast<float>(initial_y - new_grid_y));
+    transform.matrix().setFloat(1, 3, initial_y - new_grid_y);
     layer->SetTransform(transform);
 
-    // Return the first layer for the caller to observe.
-    if (!settings_to_observe)
+    if (settings)
       settings_to_observe = std::move(settings);
   }
 

ash/wm/overview/overview_session.cc

@@ -617,23 +617,25 @@ OverviewSession::UpdateGridAtLocationYPositionAndOpacity(
   if (!grid)
     return nullptr;
 
+  std::unique_ptr<ui::ScopedLayerAnimationSettings> settings =
+      grid->UpdateYPositionAndOpacity(new_y, opacity, callback);
   if (no_windows_widget_) {
-    // Translate and fade |no_windows_widget_| if it is visible.
     DCHECK(grid->empty());
+
+    // Translate and fade |no_windows_widget_| if it is visible. Overwrite
+    // |settings| to observe |no_windows_widget| if necessary.
     aura::Window* window = no_windows_widget_->GetNativeWindow();
-    std::unique_ptr<ui::ScopedLayerAnimationSettings> settings;
+    ui::Layer* layer = window->layer();
     if (!callback.is_null()) {
       settings = std::make_unique<ui::ScopedLayerAnimationSettings>(
-          window->layer()->GetAnimator());
+          layer->GetAnimator());
       callback.Run(settings.get());
     }
-    window->SetTransform(
-        gfx::Transform(1.f, 0.f, 0.f, 1.f, 0.f, static_cast<float>(-new_y)));
-    window->layer()->SetOpacity(opacity);
-    return settings;
+    window->SetTransform(gfx::Transform(1.f, 0.f, 0.f, 1.f, 0.f, -new_y));
+    layer->SetOpacity(opacity);
   }
 
-  return grid->UpdateYPositionAndOpacity(new_y, opacity, callback);
+  return settings;
 }
 
 void OverviewSession::UpdateRoundedCornersAndShadow() {