Make the progress report aligned with the single pass over the heap.

Change-Id: I6a63e7eee86719328daa588e5a0c53a668aca464
Reviewed-on: https://chromium-review.googlesource.com/1099863Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Alexei Filippov <alph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53744}