The effect of array/string trimming on space size is postponed until sweeping
completes. This simplifies runtime code and fixes live byte update race with
the concurrent marker.

This patch restores monotonicity of PromotedSinceLastGC by notify the heap
when sweeper discovers more free space than estimated.

Bug: chromium:694255
Change-Id: I7a8c24f2c3398bc0c8a43ffd1d35ace68010cd65
Reviewed-on: https://chromium-review.googlesource.com/621326
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47464}