This patch builds on previous Promise spec compliance work by
cleaning out some old code which existed to support
Promise.prototype.chain, rephrasing some code to correspond more
closely to the specification, and removing some incorrect brand
checking. A test is added for a bug in an edge case which was fixed.

R=rossberg
BUG=v8:3641
LOG=Y

Review URL: https://codereview.chromium.org/1488783002

Cr-Commit-Position: refs/heads/master@{#32627}