Add ES 3.1 version and enum to support dEQP ES 3.1 tests on Win Change supported ES version to 3.1 on win. Without GL_TEXTURE_2D_MULTISAMPLE enum, it will reach UNREACHABLE() when running dEQP ES 3.1 tests on Win. BUG=angleproject:1442 Change-Id: I55114854c4e9cba1caac10d3da5b416ef66a0d3e Reviewed-on: https://chromium-review.googlesource.com/414606 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org>