overview gesture: Fix the transient bubble dialog issue.

Turns out the bubble dialog native window is included in the MRU window
list, which seems a bug - filed a separate bug for it crbug.com/1035998.
The fix in this CL still makes sense though.

Bug: 1034653
Change-Id: I079f2256631fdd39f7102a61bd81ea4a6e88a9f0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1975086Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Xiaoqian Dai <xdai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#726549}

ash/home_screen/drag_window_from_shelf_controller.cc

@@ -36,6 +36,7 @@
 #include "ui/gfx/geometry/point_f.h"
 #include "ui/gfx/transform_util.h"
 #include "ui/wm/core/coordinate_conversion.h"
+#include "ui/wm/core/window_util.h"
 
 namespace ash {
 
@@ -76,6 +77,8 @@ class DragWindowFromShelfController::WindowsHider
     for (auto* window : windows) {
       if (window == dragged_window_)
         continue;
+      if (::wm::HasTransientAncestor(window, dragged_window_))
+        continue;
       if (!window->IsVisible())
         continue;
       if (SplitViewController::Get(window)->IsWindowInSplitView(window))