Make GL_ANGLE_instanced_arrays enableable.

BUG=angleproject:1523

Change-Id: Id1dd5d0426c1b55bfd6cca8b0c8c73596080f2a9
Reviewed-on: https://chromium-review.googlesource.com/688101
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>
diff --git a/src/libANGLE/validationES.cpp b/src/libANGLE/validationES.cpp
index 17eeb3e..9591d9e 100644
--- a/src/libANGLE/validationES.cpp
+++ b/src/libANGLE/validationES.cpp
@@ -2734,6 +2734,12 @@
                                       GLsizei count,
                                       GLsizei primcount)
 {
+    if (!context->getExtensions().instancedArrays)
+    {
+        ANGLE_VALIDATION_ERR(context, InvalidOperation(), ExtensionNotEnabled);
+        return false;
+    }
+
     if (!ValidateDrawArraysInstancedBase(context, mode, first, count, primcount))
     {
         return false;
@@ -2950,6 +2956,12 @@
                                         const void *indices,
                                         GLsizei primcount)
 {
+    if (!context->getExtensions().instancedArrays)
+    {
+        ANGLE_VALIDATION_ERR(context, InvalidOperation(), ExtensionNotEnabled);
+        return false;
+    }
+
     if (!ValidateDrawElementsInstancedBase(context, mode, count, type, indices, primcount))
     {
         return false;