Block scoped const variables.

src/messages.js

Index: src/messages.js
diff --git a/src/messages.js b/src/messages.js
index be236a4a34a95bd4ccd31bfcabfb437d87df2b3f..526e65804531472e2e932d17503c46c052392255 100644
--- a/src/messages.js
+++ b/src/messages.js
@@ -240,6 +240,7 @@ function FormatMessage(message) {
       "strict_poison_pill",           ["'caller', 'callee', and 'arguments' properties may not be accessed on strict mode functions or the arguments objects for calls to them"],
       "strict_caller",                ["Illegal access to a strict mode caller function."],
       "unprotected_let",              ["Illegal let declaration in unprotected statement context."],
+      "unprotected_const",            ["Illegal const declaration in unprotected statement context."],
       "cant_prevent_ext_external_array_elements", ["Cannot prevent extension of an object with external array elements"],
       "redef_external_array_element", ["Cannot redefine a property of an object with external array elements"],
     ];