[strong] Implement static restrictions on binding/assignment to 'undefined' identifier.

src/messages.js

Index: src/messages.js
diff --git a/src/messages.js b/src/messages.js
index e7e0938d56a8f6b117e10120ef029529e5f80062..eadba5ab05f2c2348fe2a389d28dec70d0aad7d5 100644
--- a/src/messages.js
+++ b/src/messages.js
@@ -166,6 +166,7 @@ var kMessages = {
   strict_caller:                 ["Illegal access to a strict mode caller function."],
   strong_ellision:               ["In strong mode, arrays with holes are deprecated, use maps instead"],
   strong_arguments:              ["In strong mode, 'arguments' is deprecated, use '...args' instead"],
+  strong_undefined:              ["In strong mode, binding or assigning to 'undefined' is not allowed"],

[rossberg, 2015/04/08 11:30:11]

"is not allowed" -> "is deprecated"

[conradw, 2015/04/09 12:22:22]

Done.

   strong_equal:                  ["In strong mode, '==' and '!=' are deprecated, use '===' and '!==' instead"],
   strong_delete:                 ["In strong mode, 'delete' is deprecated, use maps or sets instead"],
   strong_var:                    ["In strong mode, 'var' is deprecated, use 'let' or 'const' instead"],