Once https://chromium-review.googlesource.com/c/chromium/src/+/1351809 lands, running the disabled DifferentDeviceScaleFactorDisplayTabDragControllerTest.CursorDeviceScaleFactor results in the following on the non_single_process_mash_interactive_ui_tests stage of the linux-chromeos-rel bot:

../../chrome/browser/ui/views/tabs/tab_drag_controller_interactive_uitest.cc:2277: Failure
Expected equality of these values:
  gfx::Point(p.x, p.y)
    Which is: 399,200
  ash::Shell::Get()->aura_env()->last_mouse_location()
    Which is: 400,200
Google Test trace:
../../chrome/browser/ui/views/tabs/tab_drag_controller_interactive_uitest.cc:2270: 2

../../chrome/browser/ui/views/tabs/tab_drag_controller_interactive_uitest.cc:2279: Failure
Expected equality of these values:
  kDeviceScaleFactorExpectations[index - 1]
    Which is: 1
  test->GetCursorDeviceScaleFactor()
    Which is: 2
Google Test trace:
../../chrome/browser/ui/views/tabs/tab_drag_controller_interactive_uitest.cc:2270: 2

../../chrome/browser/ui/views/tabs/tab_drag_controller_interactive_uitest.cc:2279: Failure
Expected equality of these values:
  kDeviceScaleFactorExpectations[index - 1]
    Which is: 1
  test->GetCursorDeviceScaleFactor()
    Which is: 2
Google Test trace:
../../chrome/browser/ui/views/tabs/tab_drag_controller_interactive_uitest.cc:2270: 5

It looks to me like there are two different issues here.  The first is that the pointer is warped from x=399 to x=400, which may or may not be a bug.  If not, the test needs to be modified or account for this in some way.  This is presumably what causes the first scale factor change to occur early.

The second is that the scale factor is not changing back to 1 at the end; I don't know why.