Move function to compute the max number of threads in a TaskScheduler pool to base/.

This CL moves the formula to compute the max number of threads in a
TaskScheduler pool from components/task_scheduler_util/ to base/.
This will allow the formula to be reused in content clients
(content/renderer, content/gpu and content/utility).

TBR=danakj@chromium.org
BUG=664996

Review-Url: https://codereview.chromium.org/2501203002
Cr-Commit-Position: refs/heads/master@{#432543}
4 files changed