Add Array.prototype.reduce and .reduceRight.

src/messages.js

Index: src/messages.js
diff --git a/src/messages.js b/src/messages.js
index cd9a1e8d61ae872e396baf6a3d9daad075cf8f82..fa6fb1fc2d89988696cf48d4bcb59774e2c7b056 100644
--- a/src/messages.js
+++ b/src/messages.js
@@ -98,6 +98,7 @@ const kMessages = {
   instanceof_function_expected: "Expecting a function in instanceof check, but got %0",
   instanceof_nonobject_proto:   "Function has non-object prototype '%0' in instanceof check",
   null_to_object:               "Cannot convert null to object",
+  reduce_no_initial:            "Reduce of empty array with no initial value",
   // RangeError
   invalid_array_length:         "Invalid array length",
   invalid_array_apply_length:   "Function.prototype.apply supports only up to 1024 arguments",