Add a new invariant declaration operator.

BUG=angle:711

Change-Id: I54a48b636a68c317b8d44ee2d578847b80095289
Reviewed-on: https://chromium-review.googlesource.com/213500
Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>
diff --git a/src/compiler/translator/VariableInfo.cpp b/src/compiler/translator/VariableInfo.cpp
index 0bd95cb..54129d4 100644
--- a/src/compiler/translator/VariableInfo.cpp
+++ b/src/compiler/translator/VariableInfo.cpp
@@ -346,12 +346,7 @@
                     visitInfoList(sequence, mUniforms);
                     break;
                   default:
-                    // do not traverse invariant declarations such as
-                    //  "invariant gl_Position;"
-                    if (typedNode.getBasicType() != EbtInvariant)
-                    {
-                        visitInfoList(sequence, mVaryings);
-                    }
+                    visitInfoList(sequence, mVaryings);
                     break;
                 }