Factor formal argument parsing into ParserBase

src/messages.js

Index: src/messages.js
diff --git a/src/messages.js b/src/messages.js
index e366b9bbc1f74c53ab3883936040c4c4bf188a49..ca9d0203d44a622391b40e1dcb984ef57eeabe8c 100644
--- a/src/messages.js
+++ b/src/messages.js
@@ -200,7 +200,9 @@ var kMessages = {
   array_not_subclassable:        ["Subclassing Arrays is not currently supported."],
   for_in_loop_initializer:       ["for-in loop variable declaration may not have an initializer."],
   for_of_loop_initializer:       ["for-of loop variable declaration may not have an initializer."],
-  for_inof_loop_multi_bindings:  ["Invalid left-hand side in ", "%0", " loop: Must have a single binding."]
+  for_inof_loop_multi_bindings:  ["Invalid left-hand side in ", "%0", " loop: Must have a single binding."],
+  bad_getter_arity:              ["Getters should not have any formal parameters."],

[arv (Not doing code reviews), 2015/04/10 14:35:50]

Maybe use "must" here

Getter must not have any ...
Setter must have exactly one ...

+  bad_setter_arity:              ["Setters should only have one formal parameter."]
 };