ForLoopUnroll should only mark loops that fit the limitations in ESSL 1.00 Appendix A. BUG=angleproject:1253 TEST=angle_unittests, WebGL conformance tests Change-Id: I00b0a7d29cd42efea9611d020aa1f873ac04773f Reviewed-on: https://chromium-review.googlesource.com/317551Tested-by: Olli Etuaho <oetuaho@nvidia.com> Reviewed-by: Zhenyao Mo <zmo@chromium.org>
