[LayoutNG] Float behavior simplification before larger patch.
This is just an intermediate patch which simplifies some of the float
logic.
As we won't be "re-parenting" floats away from their actual parents
anymore a lot of the complex logic around the offsets becomes simpler.
Specifically we won't need the "paint-offset" calculation anymore.
This is just an initial patch to reduce the behaviour, it has some
regressions, but these should be fixed with the new code.
BUG=635619
Review-Url: https://codereview.chromium.org/2945213004
Cr-Commit-Position: refs/heads/master@{#483826}
6 files changed
