Add compute program compilation and linking support Compute shaders can be now compiled and linked to create programs. Some tests are added to verify successful and unsuccessful compute shader linking. The patch also replaces std::array<int, 3> with a custom struct WorkGroupSize. BUG=angleproject:1442 TEST=angle_end2end_tests TEST=angle_unittests Change-Id: I4ab0ac05755d0167a6d2a798f8d7f1516cf54d84 Reviewed-on: https://chromium-review.googlesource.com/366740 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Olli Etuaho <oetuaho@nvidia.com> Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>