Clean ChromeOS OAuth2TokenServiceDelegate of //content dependencies

This CL prepares the ChromeOS OAuth2TokenServiceDelegate for
componentization by cleaning it and its unittest of //content
dependencies.

Bug: 925830
Change-Id: I52b1901b2c6839a7a0f862e22ead40425a20d8f7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1511295
Reviewed-by: David Roger <droger@chromium.org>
Reviewed-by: Kush Sinha <sinhak@chromium.org>
Commit-Queue: Colin Blundell <blundell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#639005}
4 files changed