heap: Refactor bits in HeapObjectHeader

- Free up unusued "is free bit". This information was double encoded in
  the header.
- Use uint32_t for masks to allow the compiler to help with out of
  bounds shifts.
- Reorder declarations in HoH.

Bug: 843903
Change-Id: Ibd6a95ef9b38c41ed469f91ff07d35a0738082d1
Reviewed-on: https://chromium-review.googlesource.com/c/1350613
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610825}
1 file changed