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
R=dslomov@chromium.org

Review URL: https://codereview.chromium.org/798243004

Cr-Commit-Position: refs/heads/master@{#26084}