The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0fb00abce4d3e56ef50a1e6fc1eee947d97036f0

commit 0fb00abce4d3e56ef50a1e6fc1eee947d97036f0
Author: riajiang <riajiang@chromium.org>
Date: Fri May 26 21:20:38 2017

Keep root_location to be in pixels and display coordinates in WS.

We convert event root_location to be in screen coordinates which
mixed pixels and dip in PlatformDisplayDefault::UpdateEventRootLocation().
Then in WindowManagerState::GetRootWindowContaining(), we expect
root_location to be in screen coordinates to find the display that
event is on and mixed pixels and dip again. As root_location should
always be in pixels in window server, changing it to skip the
conversion in PlatformDisplayDefault::UpdateEventRootLocation() so
root_location remains in pixels and display coordinates after that;
and in WindowManagerState::GetRootWindowContaining(), using display
id and display coordinates to get the root_location in screen
coordinates and find the display (not actually updating root_location
to screen coordinates). mouse_pointer_last_location is also in pixels
and display coordinates now as a result as it is the same as event
root_location.

TODO: make sure this works with drag-and-drop once mouse warp is
functional with mushroom.

BUG= 701036 
TEST= mus_ws_unittests
      manual with two displays, one of which is hi-dpi
      ./out/oxygen/chrome --user-data-dir=/tmp/chrome --mus
      --screen-config=1600x900,1600x900^300/i

Review-Url: https://codereview.chromium.org/2778943005
Cr-Commit-Position: refs/heads/master@{#475133}

[modify] https://crrev.com/0fb00abce4d3e56ef50a1e6fc1eee947d97036f0/services/ui/ws/cursor_location_manager.cc
[modify] https://crrev.com/0fb00abce4d3e56ef50a1e6fc1eee947d97036f0/services/ui/ws/cursor_location_manager.h
[modify] https://crrev.com/0fb00abce4d3e56ef50a1e6fc1eee947d97036f0/services/ui/ws/display_manager.cc
[modify] https://crrev.com/0fb00abce4d3e56ef50a1e6fc1eee947d97036f0/services/ui/ws/event_dispatcher.cc
[modify] https://crrev.com/0fb00abce4d3e56ef50a1e6fc1eee947d97036f0/services/ui/ws/event_dispatcher.h
[modify] https://crrev.com/0fb00abce4d3e56ef50a1e6fc1eee947d97036f0/services/ui/ws/event_dispatcher_delegate.h
[modify] https://crrev.com/0fb00abce4d3e56ef50a1e6fc1eee947d97036f0/services/ui/ws/event_dispatcher_unittest.cc
[modify] https://crrev.com/0fb00abce4d3e56ef50a1e6fc1eee947d97036f0/services/ui/ws/platform_display_default.cc
[modify] https://crrev.com/0fb00abce4d3e56ef50a1e6fc1eee947d97036f0/services/ui/ws/platform_display_default.h
[modify] https://crrev.com/0fb00abce4d3e56ef50a1e6fc1eee947d97036f0/services/ui/ws/test_utils.h
[modify] https://crrev.com/0fb00abce4d3e56ef50a1e6fc1eee947d97036f0/services/ui/ws/window_manager_state.cc
[modify] https://crrev.com/0fb00abce4d3e56ef50a1e6fc1eee947d97036f0/services/ui/ws/window_manager_state.h
[modify] https://crrev.com/0fb00abce4d3e56ef50a1e6fc1eee947d97036f0/services/ui/ws/window_manager_state_unittest.cc

Is there more work here as part of working on hit-testing component bug 752380?

This is fixed. Kept this open to check if this works with drag-and-drop once mouse warping is wired up for mushroom but I guess we'll just file separate bugs for that. And this is not specific for the new event-targeting.