Do not expose host resolver options in HeadlessBrowserContext

... just use the command line switch instead. This is one of a steps to
prepare for the network service migration -- network service
does not expose an interface other than command line flag to configure
resolver, so we could as well let it interpret the flag directly.

Bug: 838291
Change-Id: I249beb1b64a0b5f332a1f2fa43325af2c4c0a6b6
Reviewed-on: https://chromium-review.googlesource.com/c/1258326
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Andrey Kosyakov <caseq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#596120}
11 files changed