Port: 74e38e34

Original commit message:

This adds support for computed property names, under the flag
--harmony-computed-property-names, for both object literals and
classes.

This is a revert of the revert, 7d48fd9d.

BUG=v8:3754
LOG=Y

Review URL: https://codereview.chromium.org/829913005

Cr-Commit-Position: refs/heads/master@{#26088}