Speculative fix of ash::SetBoundsInScreen() crash.

It looks like CursorManager::GetDisplay() can return an invalid display,
which then cause Shell::GetRootWindowControllerWithDisplayId(display_id)
to be a nullptr, when then cause ash::SetBoundsInScreen() crash.

Bug: 1068018
Change-Id: I8d590e146755330c94cb0934ccb57085af135e25
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2422731Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Xiaoqian Dai <xdai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#809359}

ash/wm/drag_window_resizer.cc

@@ -143,7 +143,8 @@ void DragWindowResizer::EndDragImpl() {
   // Adjust the size and position so that it doesn't exceed the size of work
   // area.
   display::Display dst_display;
-  screen->GetDisplayWithDisplayId(dst_display_id, &dst_display);
+  if (!screen->GetDisplayWithDisplayId(dst_display_id, &dst_display))
+    return;
   const gfx::Size& size = dst_display.work_area().size();
   gfx::Rect bounds = GetTarget()->bounds();
   if (bounds.width() > size.width()) {