Fix assertion failure in CollectVariables.cpp

The built-in gl_Layer can occur in the AST in cases in which either
GL_OVR_multiview or GL_OVR_multiview2 is enabled.

BUG=angleproject:2062
TEST=angle_end2end_tests

Change-Id: I7409b2712c715c3898c33300b7e5689e347742f0
Reviewed-on: https://chromium-review.googlesource.com/636367
Reviewed-by: Olli Etuaho <oetuaho@nvidia.com>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>
diff --git a/src/compiler/translator/CollectVariables.cpp b/src/compiler/translator/CollectVariables.cpp
index 8753d77..0486048 100644
--- a/src/compiler/translator/CollectVariables.cpp
+++ b/src/compiler/translator/CollectVariables.cpp
@@ -520,7 +520,8 @@
                 else
                 {
                     ASSERT(mShaderType == GL_VERTEX_SHADER &&
-                           IsExtensionEnabled(mExtensionBehavior, "GL_OVR_multiview"));
+                           (IsExtensionEnabled(mExtensionBehavior, "GL_OVR_multiview") ||
+                            IsExtensionEnabled(mExtensionBehavior, "GL_OVR_multiview2")));
                 }
                 break;
             default: