Disallow starting to drag from overview during its starting animation

Test: manual
Bug: 1012509
Change-Id: Ifd210885de279c26837f7b774ee0565b8d6d1237
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1848121Reviewed-by: Sammie Quon <sammiequon@chromium.org>
Commit-Queue: Avery Musbach <amusbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#703974}

ash/wm/overview/overview_session.cc

@@ -392,8 +392,10 @@ void OverviewSession::RemoveItem(OverviewItem* overview_item) {
 void OverviewSession::InitiateDrag(OverviewItem* item,
                                    const gfx::PointF& location_in_screen,
                                    bool is_touch_dragging) {
-  if (Shell::Get()->split_view_controller()->IsDividerAnimating())
+  if (Shell::Get()->overview_controller()->IsInStartAnimation() ||
+      Shell::Get()->split_view_controller()->IsDividerAnimating()) {
     return;
+  }
   highlight_controller_->SetFocusHighlightVisibility(false);
   window_drag_controller_ = std::make_unique<OverviewWindowDragController>(
       this, item, is_touch_dragging);

ash/wm/overview/overview_window_drag_controller.cc

@@ -137,6 +137,7 @@ OverviewWindowDragController::OverviewWindowDragController(
       is_touch_dragging_(is_touch_dragging),
       should_allow_split_view_(ShouldAllowSplitView()),
       virtual_desks_bar_enabled_(GetVirtualDesksBarEnabled(item)) {
+  DCHECK(!Shell::Get()->overview_controller()->IsInStartAnimation());
   DCHECK(!Shell::Get()->split_view_controller()->IsDividerAnimating());
 }