This is a reland of 12420537

Original change's description:
> [heap] fix Sweeper::kNumberOfSweepingSpaces
> 
> When indexing into vectors of sweeping spaces, convert the
> AllocationSpace to an index (by subtracting FIRST_GROWABLE_PAGED_SPACE)
> to avoid wasted space at the start.
> 
> Change-Id: Ia23fe6dae42d5accea9f7fe7ec5c3b303ef857b4
> Reviewed-on: https://chromium-review.googlesource.com/978242
> Reviewed-by: Hannes Payer <hpayer@chromium.org>
> Commit-Queue: Dan Elphick <delphick@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#52320}

Change-Id: Ic8ea2d58b9d4cfe97eb8efec93df101b734d5ddd
Reviewed-on: https://chromium-review.googlesource.com/994214Reviewed-by: Hannes Payer <hpayer@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52354}