Add BlockLayout doc link

Bug: 635619
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_layout_tests_layout_ng
Change-Id: I0d125fb3d1397e06566cc67e837b79559ae2f677
Reviewed-on: https://chromium-review.googlesource.com/731112
Reviewed-by: Emil A Eklund <eae@chromium.org>
Commit-Queue: Aleks Totic <atotic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512709}
1 file changed