GitLab

This changes the postTask prototype to use semantically meaningful names
and reduces the number of priorities. The priorities now match the
updated explainer:
https://github.com/WICG/main-thread-scheduling/blob/master/PrioritizedPostTask.md

The changes are:
  "immediate" --> removed. We may reconsider if we have use cases.
  "high"      --> "user-blocking"
  "default"   --> "user-visible"
  "low"       --> "background"
  "idle"      --> removed. We may also reconsider this if we have use
                  cases that can be differentiated from "background",
                  but we currently don't. This also avoids conflict w/
                  requestIdleCallback.

Bug: 979017
Change-Id: I58fb68e8bed38d8463d080bb3ff028049a69667b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2008426
Commit-Queue: Scott Haseley <shaseley@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Reviewed-by: Nate Chapin <japhet@chromium.org>
Cr-Commit-Position: refs/heads/master@{#734318}