Revert "Refactor avoidsFloats() to reflect CSS2.1 spec more clearly"

Revert of Refactor avoidsFloats() to reflect CSS2.1 spec more clearly (https://codereview.chromium.org/268833003/)

Reason for revert:
May have caused a clusterfuzz regression:
https://code.google.com/p/chromium/issues/detail?id=375954.

Original issue's description:
> Refactor avoidsFloats() to reflect CSS2.1 spec more clearly
>
> Introduce the 'createsBlockFormatting' concept to RenderBlock::avoidsFloats()
> and remove a couple of now-redundant virtualizations of the function.
>
> BUG=
>
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=173549
TBR=leviw@chromium.org

Review URL: https://codereview.chromium.org/297883002

git-svn-id: svn://svn.chromium.org/blink/trunk@174585 bbb929c8-8fbe-4397-9dbb-9b2b20218538