The test class provides facilities for parsing test shader source into
an AST and determining compile status. Compilation flags change for
some of the tests, but this should only have a minor effect on code
coverage - mostly affecting non-core parts such as intermediate
output.

BUG=angleproject:1673
TEST=angle_unittests

Change-Id: I7d0900ef490e021272a27c4b0c938bfee02abf39
Reviewed-on: https://chromium-review.googlesource.com/422367Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>