Fix app window transition to home screen

Calling OnHomeLauncherTargetPositionChanged() can change shelf bounds,
which in turn causes display work area update, and window bounds change.
With cross fade bounds update the window transition to home screen looks
broken (as cross fade creates a layer copy that is not animated).

There's an open bug to fix excessive work area updates, but in the
meantime, disabling the window animations while calling
OnHomeLauncherTargetPositionChanged() works around the issue.

BUG=1005366

Change-Id: Idf97b88204984660831cd6b025d5bdd93b7bd958
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1902480Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Reviewed-by: Manu Cornet <manucornet@chromium.org>
Commit-Queue: Toni Baržić <tbarzic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#713552}

ash/home_screen/home_screen_controller.cc

@@ -4,6 +4,7 @@
 
 #include "ash/home_screen/home_screen_controller.h"
 
+#include <memory>
 #include <vector>
 
 #include "ash/home_screen/home_launcher_gesture_handler.h"
@@ -12,6 +13,7 @@
 #include "ash/public/cpp/ash_features.h"
 #include "ash/public/cpp/shell_window_ids.h"
 #include "ash/public/cpp/window_properties.h"
+#include "ash/scoped_animation_disabler.h"
 #include "ash/session/session_controller_impl.h"
 #include "ash/shelf/shelf.h"
 #include "ash/shell.h"
@@ -157,9 +159,6 @@ bool HomeScreenController::GoHome(int64_t display_id) {
     return true;
   }
 
-  delegate_->OnHomeLauncherTargetPositionChanged(true /* showing */,
-                                                 display_id);
-
   // First minimize all inactive windows.
   const bool window_minimized =
       MinimizeAllWindows(windows, active_windows /*windows_to_ignore*/);
@@ -167,8 +166,26 @@ bool HomeScreenController::GoHome(int64_t display_id) {
   // Animate currently active windows into the home screen - they will be
   // minimized by WindowTransformToHomeScreenAnimation when the transition
   // finishes.
-
   if (!active_windows.empty()) {
+    {
+      // Disable window animations before updating home launcher target
+      // position. Calling OnHomeLauncherTargetPositionChanged() can cause
+      // display work area update, and resulting cross-fade window bounds change
+      // animation can interfere with WindowTransformToHomeScreenAnimation
+      // visuals.
+      //
+      // TODO(https://crbug.com/1019531): This can be removed once transitions
+      // between in-app state and home do not cause work area updates.
+      std::vector<std::unique_ptr<ScopedAnimationDisabler>> animation_disablers;
+      for (auto* window : active_windows) {
+        animation_disablers.push_back(
+            std::make_unique<ScopedAnimationDisabler>(window));
+      }
+
+      delegate_->OnHomeLauncherTargetPositionChanged(true /* showing */,
+                                                     display_id);
+    }
+
     base::RepeatingClosure window_transforms_callback = base::BarrierClosure(
         active_windows.size(),
         base::BindOnce(&HomeScreenController::NotifyHomeLauncherTransitionEnded,
@@ -193,8 +210,6 @@ bool HomeScreenController::GoHome(int64_t display_id) {
                                     : base::NullCallback());
       }
     }
-  } else {
-    delegate_->OnHomeLauncherAnimationComplete(true /*shown*/, display_id);
   }
 
   return window_minimized || !active_windows.empty();