Built-in JSON support

src/messages.js

Index: src/messages.js
diff --git a/src/messages.js b/src/messages.js
index fa6fb1fc2d89988696cf48d4bcb59774e2c7b056..df8a2d1d7e8aa9ac967c4810750327a6ae42602a 100644
--- a/src/messages.js
+++ b/src/messages.js
@@ -114,6 +114,9 @@ const kMessages = {
   illegal_return:               "Illegal return statement",
   error_loading_debugger:       "Error loading debugger %0",
   no_input_to_regexp:           "No input to %0",
+  result_not_primitive:         "Result of %0 must be a primitive, was %1",
+  invalid_json:                 "String '%0' is not valid JSON",
+  circular_structure:           "Converting circular structure to JSON"
 };