Check for let in lexically bound names for short object literals

Check for let in lexically bound names for short object literals

An identifier may be parsed in an object literal like {let}, but
this was previously left out of lexical name checking. This patch
adds that check to prohibit code like
  let {let} = {let: 1}

BUG=v8:4403
LOG=N
R=adamk

Committed: https://crrev.com/dd24cc33d3c26ef5548efe7967d880cd56b98278
Cr-Commit-Position: refs/heads/master@{#31278}

[Dan Ehrenberg, 2015-10-14 16:32:25]

The CQ bit was checked by littledan@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-10-14 16:32:37]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1401253003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1401253003/1

[adamk, 2015-10-14 16:35:23]

lgtm

[commit-bot: I haz the power, 2015-10-14 17:34:49]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-10-14 17:34:50]

Dry run: This issue passed the CQ dry run.

[Dan Ehrenberg, 2015-10-15 07:51:01]

The CQ bit was checked by littledan@chromium.org

[commit-bot: I haz the power, 2015-10-15 07:51:05]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1401253003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1401253003/1

[commit-bot: I haz the power, 2015-10-15 07:52:17]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-15 07:52:34]

Patchset 1 (id:??) landed as
https://crrev.com/dd24cc33d3c26ef5548efe7967d880cd56b98278
Cr-Commit-Position: refs/heads/master@{#31278}