Clear recorded slots when making a string external

Clear recorded slots when making a string external.

Slots in ConsString/SlicedString can point to an evacutaion candidate.
The MakeExternal function makes in-place conversion to external string.
After the conversion we can have a recorded slot containing an external
pointer. As long as the external pointer is aligned, this is not a
problem. We clear the recorded slots to fix verify-heap checks.

BUG=chromium:631969
LOG=NO

Finalizing CL: https://codereview.chromium.org/2199863002/

Committed: https://crrev.com/f6875cee3ab6cb69311bef765c0496877a5d3e8e
Cr-Commit-Position: refs/heads/master@{#38653}

[Michael Lippautz, 2016-08-16 11:21:04]

mlippautz@chromium.org changed reviewers:
+ jkummerow@chromium.org

[Michael Lippautz, 2016-08-16 11:21:04]

ptal.

Mainly a copy of Ulan's CL. Just fixed the lsan issue in the regression test.

[Michael Lippautz, 2016-08-16 11:21:53]

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

[commit-bot: I haz the power, 2016-08-16 11:21:56]

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

[Jakob Kummerow, 2016-08-16 11:22:49]

LGTM, thanks!

(CC'ing Ulan: FYI.)

[commit-bot: I haz the power, 2016-08-16 11:51:14]

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

[commit-bot: I haz the power, 2016-08-16 11:51:15]

Dry run: This issue passed the CQ dry run.

[Michael Lippautz, 2016-08-16 11:57:06]

The CQ bit was checked by mlippautz@chromium.org

[commit-bot: I haz the power, 2016-08-16 11:57:14]

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, 2016-08-16 11:59:14]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2016-08-16 11:59:39]

Description was changed from

==========
Clear recorded slots when making a string external.

Slots in ConsString/SlicedString can point to an evacutaion candidate.
The MakeExternal function makes in-place conversion to external string.
After the conversion we can have a recorded slot containing an external
pointer. As long as the external pointer is aligned, this is not a
problem. We clear the recorded slots to fix verify-heap checks.

BUG=chromium:631969
LOG=NO

Finalizing CL: https://codereview.chromium.org/2199863002/
==========

to

==========
Clear recorded slots when making a string external.

Slots in ConsString/SlicedString can point to an evacutaion candidate.
The MakeExternal function makes in-place conversion to external string.
After the conversion we can have a recorded slot containing an external
pointer. As long as the external pointer is aligned, this is not a
problem. We clear the recorded slots to fix verify-heap checks.

BUG=chromium:631969
LOG=NO

Finalizing CL: https://codereview.chromium.org/2199863002/

Committed: https://crrev.com/f6875cee3ab6cb69311bef765c0496877a5d3e8e
Cr-Commit-Position: refs/heads/master@{#38653}
==========

[commit-bot: I haz the power, 2016-08-16 11:59:40]

Patchset 2 (id:??) landed as
https://crrev.com/f6875cee3ab6cb69311bef765c0496877a5d3e8e
Cr-Commit-Position: refs/heads/master@{#38653}