async/await: Don't trigger uncaught rejection handlers on throwaway Promises

async/await: Don't trigger uncaught rejection handlers on throwaway Promises

This patch implements a bug fix to the async/await specification described
at https://github.com/tc39/ecma262/pull/692#issuecomment-247488411
Namely, the intermediate values of Promises may be rejected, and they do
not have .then called on them anymore (now that the memory leak is fixed),
but they do not correspond do unhandled rejections. This change has been
tested manually with integration with Blink; once it is checked in and
rolled, then further tests can be added on the Blink side for the uncaught
rejection handler and async/await.

BUG=v8:4483
Committed: https://crrev.com/61a6b6f236079927a0e9640742fe4b0c282a9d09
Cr-Commit-Position: refs/heads/master@{#39480}

[Dan Ehrenberg, 2016-09-16 19:06:15]

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

[commit-bot: I haz the power, 2016-09-16 19:06:20]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[Dan Ehrenberg, 2016-09-16 19:06:44]

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

[domenic, 2016-09-16 19:12:25]

Non-reviewer LGTM. Note that there's the potential for further future
optimizations/fixes by getting rid of the throwaway promise, but that definitely
belongs in a follow-up, preferably after the spec has also been updated
(https://github.com/tc39/ecma262/issues/694).

[commit-bot: I haz the power, 2016-09-16 19:35:43]

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

[commit-bot: I haz the power, 2016-09-16 19:35:44]

Dry run: This issue passed the CQ dry run.

[adamk, 2016-09-16 20:13:55]

lgtm

[Dan Ehrenberg, 2016-09-16 20:20:25]

The CQ bit was checked by littledan@chromium.org

[commit-bot: I haz the power, 2016-09-16 20:20:32]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-09-16 20:23:09]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-09-16 20:23:59]

Description was changed from

==========
async/await: Don't trigger uncaught rejection handlers on throwaway Promises

This patch implements a bug fix to the async/await specification described
at https://github.com/tc39/ecma262/pull/692#issuecomment-247488411
Namely, the intermediate values of Promises may be rejected, and they do
not have .then called on them anymore (now that the memory leak is fixed),
but they do not correspond do unhandled rejections. This change has been
tested manually with integration with Blink; once it is checked in and
rolled, then further tests can be added on the Blink side for the uncaught
rejection handler and async/await.

BUG=v8:4483
==========

to

==========
async/await: Don't trigger uncaught rejection handlers on throwaway Promises

This patch implements a bug fix to the async/await specification described
at https://github.com/tc39/ecma262/pull/692#issuecomment-247488411
Namely, the intermediate values of Promises may be rejected, and they do
not have .then called on them anymore (now that the memory leak is fixed),
but they do not correspond do unhandled rejections. This change has been
tested manually with integration with Blink; once it is checked in and
rolled, then further tests can be added on the Blink side for the uncaught
rejection handler and async/await.

BUG=v8:4483

Committed: https://crrev.com/61a6b6f236079927a0e9640742fe4b0c282a9d09
Cr-Commit-Position: refs/heads/master@{#39480}
==========

[commit-bot: I haz the power, 2016-09-16 20:24:01]

Patchset 1 (id:??) landed as
https://crrev.com/61a6b6f236079927a0e9640742fe4b0c282a9d09
Cr-Commit-Position: refs/heads/master@{#39480}