Include the tools/android/errorprone_plugin mirror. This eliminates
several cloned source files from ANGLE. Also include the Python
tools/swarming_client for running tests. It seems like the tests
depend on the logdog Python library available from this component.

Bug: angleproject:2344
Change-Id: I70e011764c4443ab3904bfa0c9059f295f3817df
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2845233Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>