The ES6 specification does not explicitly state the attributes for the
'next' and 'throw' property descriptors, so their values are defined by
Section 17 [1]:

> Every other data property described in clauses 18 through 26 and in
> Annex B.2 has the attributes
> { [[Writable]]: true, [[Enumerable]]: false, [[Configurable]]: true }
> unless otherwise specified.

[1]
https://people.mozilla.org/~jorendorff/es6-draft.html#sec-ecmascript-standard-built-in-objects

BUG=v8:3986
LOG=N
R=wingo,arv

Review URL: https://codereview.chromium.org/1051363003

Cr-Commit-Position: refs/heads/master@{#27770}