The spec tests are stored on a mirror and are downloaded with the DEPS
file. The test files on the mirror are updated with a script which has
to be executed manually.

This CL contains the following changes:

* A script which updates the spec tests and uploads the generated files
  to the mirror.
* Changes to the DEPS file to download the files from the mirror.
* Changes so that tools/run-tests.py can run the spec tests.

R=machenbach@chromium.org, rossberg@chromium.org

Change-Id: Ia50d09bb1501c0c0f1d1506aa3657a3aa69c2864
Reviewed-on: https://chromium-review.googlesource.com/488083
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44933}