[scheduler] Move stop-non-timers-in-background flag to blink features

The StopNonTimersInBackground flag is used by scheduler to initialize
the freezable bits for tasks. This happens before Blink initialization,
so the flag wasn't set yet when initializing QueueTraits. This CL moves
the flag from runtime enabled features to blink features, which are
initialized earlier and can be checked directly during QueueTraits
initialization.

BUG: 859963

Change-Id: I62e9896cd3c75a04d23372b44e9697432d109088
Reviewed-on: https://chromium-review.googlesource.com/1159205
Reviewed-by: Alexander Timin <[email protected]>
Reviewed-by: Kinuko Yasuda <[email protected]>
Commit-Queue: Scott Haseley <[email protected]>
Cr-Commit-Position: refs/heads/master@{#580540}
12 files changed