There is no need to add speed-bumps for incremental marking purposes
for allocations from CompactionSpaces. This path was getting reached
for Parallel Scavenges.

Bug: 
Change-Id: I1f0f315549206bc86f8c48e202c29c18d212369b
Reviewed-on: https://chromium-review.googlesource.com/617920Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Ali Ijaz Sheikh <ofrobots@google.com>
Cr-Commit-Position: refs/heads/master@{#47408}