[LayoutNG] Fix clearance offset for floats.

I was beginning to make our floats immutable, and noticed that we were
calculating the clearance offset wrong. This fixes and removes a bunch
of unused functionality in preparation for the immutable patch.

Bug: 635619
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_layout_tests_layout_ng
Change-Id: Ic005486798e9803a2fee79033d8bf1b4e33de540
Reviewed-on: https://chromium-review.googlesource.com/612489
Commit-Queue: Ian Kilpatrick <ikilpatrick@chromium.org>
Reviewed-by: Emil A Eklund <eae@chromium.org>
Cr-Commit-Position: refs/heads/master@{#493879}
9 files changed