The heap profiler randomly crashed because of memory corruption caused
by unexpected heap objects layout changes occured between count and fill
passes. The changes lead the number of retainers counted on the first pass
did not match its number on the fill pass leading to the out of bounds
array access.

Besides that the mark bit scheme has been changed to a plain vector one in
dominators building algorithm. It is up to 4x faster because of smaller
memory access footprint.

BUG=
TEST=

Review URL: https://chromiumcodereview.appspot.com/9594020
Patch from Alexei Filippov <alexeif@chromium.org>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10928 ce2b1a6d-e550-0410-aec6-3dcde31c8c00