ES6 computed property names

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, a76419f0f497db156eb1010e9b4be398951280cb.

This changes to do an early bailout in
HOptimizedGraphBuilder::VisitObjectLiteral instead of doing that in the later
loop.

BUG=v8:3754
LOG=Y
TBR=dslomov@chromium.org

Review URL: https://codereview.chromium.org/792233008

Cr-Commit-Position: refs/heads/master@{#25868}