recording the damage when we reflow the floater. This allows us to
catch several cases that we weren't catching before, so we no longer
need to dirty all the line boxes when an incremental reflow targeted
at a float arrives. r=dbaron, sr=attinasi.
git-svn-id: svn://10.0.0.236/trunk@119985 18797224-902f-48f8-a5cc-f745e15eee43
