The new TestRuleProcess test tests the full rule-processing paths.
The test fixture reduces code duplication.

Bug: angleproject:2993

Change-Id: Ia07ea408fb771dfd1a21cc2fd4610e0e88f529ea
Reviewed-on: https://chromium-review.googlesource.com/c/1366314
Commit-Queue: Ian Elliott <ianelliott@google.com>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>