Image annotation service: provide Google API key in requests to server.

In order to prevent abuse of the image annotation server, we authenticate
communication using Chrome's Google API key.

We also add tests for a Google utility function, to verify it works for
our use case.

Bug: 916420
Change-Id: Id30561c7a0c08c97bbfa8dcafa5b0d0384821b5e
Reviewed-on: https://chromium-review.googlesource.com/c/1475011
Commit-Queue: Michael Martis <martis@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Reviewed-by: David Roger <droger@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Andrew Moylan <amoylan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#632999}
10 files changed