[LayoutNG] Refactor of exclusion space.

This pulls the previous "NGExclusions" struct into a "NGExclusionSpace"
class, and moves a bunch of utility methods onto it.

Bug: 635619
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_layout_tests_layout_ng
Change-Id: Ic9d600c759d4822f9d702c918297c014b250ec5c
Reviewed-on: https://chromium-review.googlesource.com/612623
Commit-Queue: Ian Kilpatrick <ikilpatrick@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#494110}
18 files changed