GitLab

Make views::Widget::InitParams::context optional. This cuts some
dependencies between //chrome/browser/ui and //ash, which we need to
do for go/mustash.

Change the default display for windows that supply neither parent nor
context to the "root window for new windows" (i.e. the display where
the user last activated a window). The old behavior was to always use
the primary display. The new behavior is consistent with mash.

Fix a couple cases where windows were defaulting to the primary
display when they should have been using the display for new windows
(e.g. task manager when all browsers are closed).

Bug: 826569
Test: covered by tests
Change-Id: I4571c3c7066b4247559d43e7b1192ef8411f8919
Reviewed-on: https://chromium-review.googlesource.com/988732
Commit-Queue: James Cook <jamescook@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#547515}