Promise.then should not throw a TypeError on ground of parameters.

Promise.prototype.then should not throw a TypeError if non-callable
values (e.g. as null, 0, "hello") are given.

BUG=326093

Review URL: https://codereview.chromium.org/106373002

git-svn-id: svn://svn.chromium.org/blink/trunk@163286 bbb929c8-8fbe-4397-9dbb-9b2b20218538