GitLab

With this change, I introduce the notion of element bounds. Previously,
the only non-inherited geometric info an element owned was its size.
Now we also store its position. The non-inherited, local size and
transform are stored jointly in a bounds rect.

I've also made the updating of layout a non-virtual function that calls
out to a virtual layout function in order to guarantee that the
UiElement has an opportunity to update its bounds following the layout
of its children.

Bug: None
Change-Id: Ia6bb9bda6008a8aaf9e5dc4c70940dec2f7d73b7
Reviewed-on: https://chromium-review.googlesource.com/763650
Commit-Queue: Ian Vollick <vollick@chromium.org>
Reviewed-by: Biao She <bshe@chromium.org>
Cr-Commit-Position: refs/heads/master@{#515734}