There are multiple failures in the scenario.

First, the test scenario calls 'SetBounds' to move the browser window so that it still resides within the primary screen but majority of the window is covered by the secondary screen. However, this bounds change does not take effect with Mash because of the window hierarchical differences.

browser()->window()->SetBounds() or similar will be okay, although this type of setting bounds will move the window to the secondary display since majority of the window overlaps with the secondary display.

As far as I checked the original intent of the test case, maybe we want to write the drag behavior to place the window instead of calling SetBounds.

However, after changing like that, it still fails -- the dragged window still resides in the primary display (fail at https://cs.chromium.org/chromium/src/chrome/browser/ui/views/tabs/tab_drag_controller_interactive_uitest.cc?q=chrome/browser/ui/views/tabs/tab_drag_&sq=package:chromium&g=0&l=2039). Needs to investigate why.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/2712c58b1c0bcaae9c520bea65710a0bb01b1de7

commit 2712c58b1c0bcaae9c520bea65710a0bb01b1de7
Author: Jun Mukai <mukai@chromium.org>
Date: Tue Nov 06 18:00:46 2018

Fix of DragBrowserWindowWhenMajorityOfBoundsInSecondDisplay for Mash

This CL fixes DragBrowserWindowWhenMajorityOfBoundsInSecondDisplay
of tab-dragging for Mash;
- SetBounds are not great for testing with Mash since it may not
  reflect the correct location in Ash, or it may cause moving the
  browser window to the secondary display. Instead, dragging events
  to move the browser window which still resides in the primary
  display but covers on the secondary display.
- Creates a mouse move event on the warped pointer; as far as
  I debugged, this is not happening in the classic environment
  too, but the test was passing somehow (the newly added expectation
  of browser bounds at the end fails even without Mash).

BUG= 901543 
TEST=trybot

Change-Id: Id4826673975535e0dc12460cda4a62b060a328db
Reviewed-on: https://chromium-review.googlesource.com/c/1318794
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Commit-Queue: Jun Mukai <mukai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605734}
[modify] https://crrev.com/2712c58b1c0bcaae9c520bea65710a0bb01b1de7/chrome/browser/ui/views/tabs/tab_drag_controller_interactive_uitest.cc
[modify] https://crrev.com/2712c58b1c0bcaae9c520bea65710a0bb01b1de7/testing/buildbot/filters/chromeos.single_process_mash.interactive_ui_tests.filter