Fix showing the sibling menu on mouse move

ash/display/screen_ash.cc

Index: ash/display/screen_ash.cc
diff --git a/ash/display/screen_ash.cc b/ash/display/screen_ash.cc
index c6a2847c2cdbacd4d500bedb751f39930272beec..e20fec801c44ff649683c0ec3b91c1cff4f59765 100644
--- a/ash/display/screen_ash.cc
+++ b/ash/display/screen_ash.cc
@@ -104,7 +104,7 @@ gfx::NativeWindow ScreenAsh::GetWindowAtScreenPoint(const gfx::Point& point) {
   if (position_client)
     position_client->ConvertPointFromScreen(root_window, &local_point);
 
-  return root_window->GetTopWindowContainingPoint(local_point);

[afakhry, 2017/03/21 17:35:47]

+Sadrul.

Oshima and talked about deprecating this GetTopWindowContainingPoint() as it is
not used in many places but we want to confirm that its use here in this context
is wrong. WDYT?

[sadrul, 2017/03/22 20:04:31]

Can you clarify how this change fixes the bug you are trying to fix (and what is
causing the bug in the first place)?

If GetTopWindowContainingPoint() ends up not being necessary, then yes please!
rm-rf code not used/necessary.

[afakhry, 2017/03/22 20:29:33]

Thanks.

GetTopWindowContaingPoint() on ARC++ devices return the ExoShellSurface window
rather than the window that's the owner widget of the window controller.
Resulting in returning early here
https://cs.chromium.org/chromium/src/ui/views/controls/menu/menu_controller.c...
without showing the sibling window.

More details are in this comment on the bug:
https://bugs.chromium.org/p/chromium/issues/detail?id=594439#c28

+  return root_window->GetEventHandlerForPoint(local_point);
 }
 
 int ScreenAsh::GetNumDisplays() const {