Guard @@isConcatSpreadable behind a flag

Guard @@isConcatSpreadable behind a flag

The breakage to Chrome seems to be based on @@isConcatSpreadable
and turning that part off with this patch fixes the Maps Tips & Tricks
test case.

BUG=chromium:507553
LOG=Y
R=adamk

Committed: https://crrev.com/a415f594585cb16cd1b4067cab905ddab61c6e5b
Cr-Commit-Position: refs/heads/master@{#29545}

[Dan Ehrenberg, 2015-07-08 21:01:54]

littledan@chromium.org changed reviewers:
+ adamk@chromium.org

[adamk, 2015-07-08 21:08:19]

Code lgtm, but you'll need to add the --harmony-concat-spreadable flag to
test/mjsunit/harmony/array-concat.js

[caitp (gmail), 2015-07-08 21:09:56]

On 2015/07/08 21:01:55, Dan Ehrenberg wrote:

What specifically breaks WRT isConcatSpreadable? Iirc we have confidence there's
no missing AC security issue, and it should be pretty close to spec. I'll take a
look in a little bit

[adamk, 2015-07-08 21:10:34]

https://codereview.chromium.org/1226063002/diff/20001/src/harmony-concat-spre...
File src/harmony-concat-spreadable.js (right):

https://codereview.chromium.org/1226063002/diff/20001/src/harmony-concat-spre...
src/harmony-concat-spreadable.js:12: // TODO(dslomov, caitp): Move to symbol.js
when shipping
Maybe change this TODO's attribution while you're in here.

[Dan Ehrenberg, 2015-07-08 21:10:47]

The CQ bit was checked by littledan@chromium.org

[Dan Ehrenberg, 2015-07-08 21:10:47]

The patchset sent to the CQ was uploaded after l-g-t-m from adamk@chromium.org
Link to the patchset: https://codereview.chromium.org/1226063002/#ps40001
(title: "Fix harmony/array-concat test to pass new flag")

[Dan Ehrenberg, 2015-07-08 21:10:54]

The CQ bit was unchecked by littledan@chromium.org

[Dan Ehrenberg, 2015-07-08 21:12:22]

The CQ bit was checked by littledan@chromium.org

[Dan Ehrenberg, 2015-07-08 21:12:22]

The patchset sent to the CQ was uploaded after l-g-t-m from adamk@chromium.org
Link to the patchset: https://codereview.chromium.org/1226063002/#ps80001
(title: "change todo again")

[commit-bot: I haz the power, 2015-07-08 21:12:44]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1226063002/80001

[Dan Ehrenberg, 2015-07-08 21:13:25]

On 2015/07/08 21:09:56, caitp wrote:
> On 2015/07/08 21:01:55, Dan Ehrenberg wrote:
> 
> What specifically breaks WRT isConcatSpreadable? Iirc we have confidence
there's
> no missing AC security issue, and it should be pretty close to spec. I'll take
a
> look in a little bit

I have no idea. Unless someone looks up Symbol.isConcatSpreadable and assigns
that property, it shouldn't change anything (for example, TypedArrays are not
concat spreadable). I just know that this is what's causing the Chrome breakage.

[Dan Ehrenberg, 2015-07-08 21:13:27]

On 2015/07/08 21:09:56, caitp wrote:
> On 2015/07/08 21:01:55, Dan Ehrenberg wrote:
> 
> What specifically breaks WRT isConcatSpreadable? Iirc we have confidence
there's
> no missing AC security issue, and it should be pretty close to spec. I'll take
a
> look in a little bit

I have no idea. Unless someone looks up Symbol.isConcatSpreadable and assigns
that property, it shouldn't change anything (for example, TypedArrays are not
concat spreadable). I just know that this is what's causing the Chrome breakage.

[Dan Ehrenberg, 2015-07-08 21:14:58]

The CQ bit was unchecked by littledan@chromium.org

[adamk, 2015-07-08 21:15:48]

One more thought (sorry for the extra back-and-forth): what if we leave this
staged? That'll let us continue to pass any test262 tests that exercise it.

[Dan Ehrenberg, 2015-07-08 21:24:31]

On 2015/07/08 21:15:48, adamk wrote:
> One more thought (sorry for the extra back-and-forth): what if we leave this
> staged? That'll let us continue to pass any test262 tests that exercise it.

Done

[Dan Ehrenberg, 2015-07-08 21:24:34]

The CQ bit was checked by littledan@chromium.org

[Dan Ehrenberg, 2015-07-08 21:24:35]

The patchset sent to the CQ was uploaded after l-g-t-m from adamk@chromium.org
Link to the patchset: https://codereview.chromium.org/1226063002/#ps100001
(title: "stage new option so test262 passes")

[commit-bot: I haz the power, 2015-07-08 21:24:49]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1226063002/100001

[commit-bot: I haz the power, 2015-07-08 21:49:49]

Committed patchset #6 (id:100001)

[commit-bot: I haz the power, 2015-07-08 21:50:11]

Patchset 6 (id:??) landed as
https://crrev.com/a415f594585cb16cd1b4067cab905ddab61c6e5b
Cr-Commit-Position: refs/heads/master@{#29545}