ES31: Add PROGRAM_SEPARABLE to ProgramParameter and GetProgram

BUG=angleproject:1939
TEST=angle_end2end_tests

Change-Id: I97ad11360f7c015947a2c0cc7d4a47f994726834
Reviewed-on: https://chromium-review.googlesource.com/454264
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
diff --git a/src/libANGLE/validationES.cpp b/src/libANGLE/validationES.cpp
index 74037b2..705e170 100644
--- a/src/libANGLE/validationES.cpp
+++ b/src/libANGLE/validationES.cpp
@@ -5191,6 +5191,14 @@
             }
             break;
 
+        case GL_PROGRAM_SEPARABLE:
+            if (context->getClientVersion() < Version(3, 1))
+            {
+                context->handleError(Error(GL_INVALID_ENUM, "Querying requires at least ES 3.1."));
+                return false;
+            }
+            break;
+
         default:
             context->handleError(Error(GL_INVALID_ENUM, "Unknown parameter name."));
             return false;