Fix shaders with invariant keyword.

We would trigger assertion failures in Debug mode, and fail to
parse and translate correctly in Release.

BUG=angle:711

Change-Id: Ibb7f33b288376617598578f48c7bbdbdec044279
Reviewed-on: https://chromium-review.googlesource.com/210822
Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Nicolas Capens <capn@chromium.org>
diff --git a/src/compiler/translator/util.cpp b/src/compiler/translator/util.cpp
index 85c89ca..46ce99c 100644
--- a/src/compiler/translator/util.cpp
+++ b/src/compiler/translator/util.cpp
@@ -268,6 +268,8 @@
       case EvqFragmentIn:
       case EvqVaryingIn:
       case EvqVaryingOut:
+      case EvqInvariantVaryingIn:
+      case EvqInvariantVaryingOut:
         return INTERPOLATION_SMOOTH;
 
       case EvqCentroidIn: