overview gesture: fix the hotseat jumping during window dragging.

Hotseat is placed differently in overview and out overview, thus can
cause jumping when overview is opened behind the dragged window. Make
sure it's not jumping during dragging.

Bug: 997885
Change-Id: Idc9d96cda431b6a1a3a0e039a918bcfb2f493776
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1879823Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Xiaoqian Dai <xdai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#709493}

ash/shelf/shelf_layout_manager.cc

@@ -1601,7 +1601,8 @@ void ShelfLayoutManager::UpdateTargetBoundsForGesture(
 
     int hotseat_y = 0;
     if (!Shell::Get()->overview_controller() ||
-        !Shell::Get()->overview_controller()->InOverviewSession()) {
+        !Shell::Get()->overview_controller()->InOverviewSession() ||
+        window_drag_controller_) {
       const int hotseat_extended_y =
           Shell::Get()->shelf_config()->hotseat_size() +
           Shell::Get()->shelf_config()->hotseat_bottom_padding();