GitLab

WindowSizerAsh needs synchronous access to the target display for each
new browser window.

* Create ash::ShellState and move root_window_for_new_windows_ there
* Introduce mojom::ShellState interface in ash
* Create a ShellStateClient in chrome to cache the target display id
  for new windows

The interface is not implemented by ash::Shell because ash::Shell
is already massive (1500 lines). Also, shell.h is included in 900
places in the code base and I don't want to add mojo generated headers
to shell.h.

Windows still don't appear on the secondary display with
--enable-features=Mash, but chrome is getting the correct display
id and setting the window bounds properly. I think ash needs to be
fixed to support top-level bounds on the secondary display, but that
will need to be a follow-up CL.

Bug: 764009, 768908
Test: ash_unittests, unit_tests for WindowSizer
Change-Id: Ib77834f8ed5dc4e65f02ff83ab81acbf3331db61
Reviewed-on: https://chromium-review.googlesource.com/1067591Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Evan Stade <estade@chromium.org>
Commit-Queue: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#561950}