Finish making FloatingObject a real class with private members

Finish making FloatingObject a real class with private members

Previously FloatingObject was in a half-done state where
it had accessors for many members, but also many members
were public.

This CL makes all members private and adds the necessary remaining
accessors.

As I toured the float code (while writing this CL) it became clear
to me that this code is very fragile/dangerous and needs to have
better memory management, and see if we can get away with not
having all these raw pointers to other renders (or lineboxes!)
which if we're not careful could go stale during a layout or style resolve.

BUG=271774
R=zoltan@adobe.com

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=155964

[Zoltan, 2013-08-12 23:21:39]

The change looks good to me. 
Do we have an issue to track the floats refactoring work?

[eseidel, 2013-08-12 23:27:58]

No, but I'm happy to make one.

[Zoltan, 2013-08-12 23:30:19]

lgtm

[eseidel, 2013-08-12 23:35:03]

Committed patchset #1 manually as r155964 (presubmit successful).