[layoutng] Implement operator== for constraint spaces

This is a prerequisite for fragment caching, because we
only want to reuse a fragment if the constraint space
hasn't changed.

Bug: 591099
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_layout_tests_layout_ng
Change-Id: Ice9bfa8fe2a9cc013997ab92d31e4f1b2df4ea45
Reviewed-on: https://chromium-review.googlesource.com/517203
Commit-Queue: Christian Biesinger <cbiesinger@chromium.org>
Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#478409}
4 files changed