GitLab

In theory, views::Widget::ReparentNativeView and
views::Widget::InitParams allow specifying any NSView* as the parent of
a views::Widget.

The only parent ever actually specified in production is the NSView*
corresponding to the root views::View of another views::Widget.

Add a CHECK to verify that this is the case. If the CHECK is not hit,
then we remove this functionality. Continue to allow testing of this
path (for now) by disabling this CHECK via a static method.

Bug: 859152
Change-Id: I70a9a22352e22b1949d37c86c36388ed5380316b
Reviewed-on: https://chromium-review.googlesource.com/1255863
Commit-Queue: ccameron <ccameron@chromium.org>
Reviewed-by: Trent Apted <tapted@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595752}