GitLab

* Shorten code
* Use helpers for repeated code
* Fix case where we checked one child's classname, then cast a different child
* Use base::size()
* Use std::make_unique()
* Use base::nullopt
* Use View::Views
* constexpr kConstant
* Make GridLayoutTest.FixedSize consistent about loop nesting order
* Make ViewTest.ChildViewZOrderChanged consistent about checking children, then
  layers

Bug: none
Change-Id: I871af00669e629176aa8fd2cc4cac2736629b3f0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1575166
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Michael Wasserman <msw@chromium.org>
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#652712}