When an iterable object is passed in as the argument to the Map and Set
constructor the elements of the iterable object are used to populate the
Map and Set.

http://people.mozilla.org/~jorendorff/es6-draft.html#sec-map-iterable
http://people.mozilla.org/~jorendorff/es6-draft.html#sec-set-iterable

BUG=v8:3398
LOG=Y
R=rossberg@chromium.org

Review URL: https://codereview.chromium.org/345613003

Patch from Erik Arvidsson <arv@chromium.org>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21950 ce2b1a6d-e550-0410-aec6-3dcde31c8c00