Revert 154327 "Fix performance regression from Blink r154194."

Still causing perf issues.

> Fix performance regression from Blink r154194.
> 
> Change in Blink r154194 caused perf regression on tests that use many floating
> objects.
> 
> This change reduces the overhead of clearFloats(), at the cost of leaving
> obsolete container references in the floating object container map. These
> references are cleared when the float or the containing RenderBlock is
> deleted. In most cases when these references are being removed, they will be
> re-added again during layout anyway.
> 
> BUG=260286
> R=inferno@chromium.org
> 
> Review URL: https://chromiumcodereview.appspot.com/19240005

TBR=kenrb@chromium.org

Review URL: https://codereview.chromium.org/21406002

git-svn-id: svn://svn.chromium.org/blink/trunk@155273 bbb929c8-8fbe-4397-9dbb-9b2b20218538