This patch intends to implement glSampleMaski on OpenGL backends. Refers to: https://chromium-review.googlesource.com/c/487603 BUG=angleproject:1592 TEST=dEQP-GLES31.functional.state_query.*.sample_mask* TEST=dEQP-GLES31.functional.texture.multisample.*.sample_mask* Change-Id: If5ddd6ab57259593919a482be80fbdbe29f6f54d Reviewed-on: https://chromium-review.googlesource.com/573727 Commit-Queue: Corentin Wallez <cwallez@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org>
