overview: Fix bug with close button showing up when tapping with 2nd finger.

Test: manual
Bug: 872106
Change-Id: I7c1e1f7f29ed1fac749b0ed5808d7f753cad7de5
Reviewed-on: https://chromium-review.googlesource.com/1179973Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584104}

ash/wm/overview/window_selector_item.cc

@@ -818,10 +818,10 @@ void WindowSelectorItem::ActivateDraggedWindow() {
 }
 
 void WindowSelectorItem::ResetDraggedWindowGesture() {
-  OnSelectorItemDragEnded();
   if (!IsDragItem())
     return;
 
+  OnSelectorItemDragEnded();
   window_selector_->ResetDraggedWindowGesture();
 }