This CL makes angle_test() use an angle-specific gtest launcher -
AngleUnitTestActivity.java. This enables building standalone Android
angle without //base

Chromium-Bug: 1149922
Bug: None
Change-Id: Id84f3e2bd84c5017ed1988ca07534f424ebfa596
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2745535Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>