- Create getters for number of tasks for all parallel stages
- Count slots for the minor MC and limit tasks by the overall number of slots.
- Cleanup existing getters.

Bug: chromium:651354
Change-Id: I9f67cca4474cbe1800faff4a549fbec019b096ce
Reviewed-on: https://chromium-review.googlesource.com/512862
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45513}