Refactor translating a ESSL shader string into a target language so that compiler initialization and cleanup code can be reused between test classes. BUG=angleproject:817 TEST=angle_unittests Change-Id: Idb229dceb9e17b13ed6ad2a68ab55ed5c968780e Reviewed-on: https://chromium-review.googlesource.com/275814Tested-by: Olli Etuaho <oetuaho@nvidia.com> Reviewed-by: Jamie Madill <jmadill@chromium.org>
