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=
R=weiliang.lin@intel.com

Review URL: https://codereview.chromium.org/825593004

Cr-Commit-Position: refs/heads/master@{#26090}