Expose chrome-proxy header to the UI thread

Adds a callback to DRPRequestOptions which forwards the CP header to
DRPService via DRPIOData.

Bug: 864187
Change-Id: I3c326386986a73cdbad418fa06783de4e6f3b239
Reviewed-on: https://chromium-review.googlesource.com/1138979
Commit-Queue: Robert Ogden <robertogden@chromium.org>
Reviewed-by: Ryan Sturm <ryansturm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575482}
6 files changed