This patch adds a concurrent marking deque that exposes the same interface
for the main thread as the existing marking deque.

The matching interface makes the concurrent marking deque a drop-in
replacement for the sequential marking deque without any change in
mark-compactor and incremental marker.

BUG=chromium:694255

Review-Url: https://codereview.chromium.org/2810893002
Cr-Commit-Position: refs/heads/master@{#45042}