[EoS] Add country code to the request for the catalog.

The country code comes from the first place in the following list with a
non-empty country code:
* Field Trial parameter "country_override", configurable by Finch server
* Finch permanent country, which is updated when the Finch configs are
  updated (by default once per Chrome version). Permanent country may
  not be available in the first run of Chrome.
* Finch latest country, which is available on every run of Chrome.

Bug: 867488
Change-Id: I0e407a50a4020882152dda85935ecf843a000cb0
Reviewed-on: https://chromium-review.googlesource.com/c/1256110
Commit-Queue: Justin DeWitt <dewittj@chromium.org>
Reviewed-by: Peter Williamson <petewil@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595978}
4 files changed