Implement get compute work group size for glGetProgramiv

BUG=angleproject:2187
TEST=dEQP-GLES31.functional.state_query.program.compute_work_group_size_get_programiv

Change-Id: Ic09153ffccfb207e37ad70cf7e14714be987e7e1
Reviewed-on: https://chromium-review.googlesource.com/722178
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
diff --git a/src/libANGLE/validationES.cpp b/src/libANGLE/validationES.cpp
index 9591d9e..4a19e9a 100644
--- a/src/libANGLE/validationES.cpp
+++ b/src/libANGLE/validationES.cpp
@@ -4151,6 +4151,7 @@
             break;
 
         case GL_PROGRAM_SEPARABLE:
+        case GL_COMPUTE_WORK_GROUP_SIZE:
             if (context->getClientVersion() < Version(3, 1))
             {
                 ANGLE_VALIDATION_ERR(context, InvalidEnum(), ES31Required);