GitLab

This CL adds a new set of tests for the reauth dialog. These tests
check interactions with a Gaia Reauth endpoint that is imitated through
an EmbeddedTestServer.

The main "embedded/xreauth/chrome" endpoint operates in two modes:
- In the default mode, the endpoint redirects to the "challenge" URL
whose response can be controlled within the test by a
ControllableHttpResponse.
- If the "?done" query is present, the endpoint returns the
HTTP_NO_CONTENT response that signifies a successful reauth.

The CL also extracts common test code into test suite functions to
reduce the code duplication and make the tests code more readable.

Bug: 1045515
Change-Id: I89d4aac57ef25168def1341fb63b1a7498dcfa0f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2225396
Commit-Queue: Alex Ilin <alexilin@chromium.org>
Reviewed-by: David Roger <droger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#774205}