Do not get TaskScheduler field trial params from command line in renderers.

base::GetFieldTrialParams() used not to work in child processes. For
that reason, we built a system to pass scheduler field trial params
to renderers on the command line. Now that base::GetFieldTrialParams()
works fine in child processes
(https://cs.chromium.org/chromium/src/content/app/content_main_runner.cc?l=160&rcl=9030625190ec0a2b60be2af279bcb234f47d3f51),
we don't need to use that system anymore.

[email protected]

Bug: 810049
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: Ic40653eece1a103a9c913cb286925061fed1121c
Reviewed-on: https://chromium-review.googlesource.com/909169
Commit-Queue: François Doray <[email protected]>
Reviewed-by: Scott Violet <[email protected]>
Reviewed-by: Robert Liao <[email protected]>
Cr-Commit-Position: refs/heads/master@{#537305}
7 files changed