Resource Scheduler: Add metrics to record gap between non-delayable requests

Change-Id: If2df199cac0efd9f3293427aee5557f78e99a2e2
Bug: 935703
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1491133
Commit-Queue: Tarun Bansal <tbansal@chromium.org>
Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Reviewed-by: Doug Arnett <dougarnett@chromium.org>
Cr-Commit-Position: refs/heads/master@{#637353}
3 files changed