Fix String16's move constructor

Fix String16's move constructor

String16 had a pseudo move constructor that took a const String16&&. The
problem with this is that the point of moving objects is the ability to
clobber the underlying data. If we look at this particular case, the
move ctor tried to then std::move the underlying std::basic_string<>;
this results in passing a const std::basic_string<>&& to the
basic_string ctor. This resolves to the const std::basic_string<>&
*copy* ctor. So in the end, we haven't moved anything.

Fix this by taking a mutable rvalue reference that allows the moving to
work as expected.

BUG=None

Review-Url: https://codereview.chromium.org/2616973002
Cr-Commit-Position: refs/heads/master@{#42147}
Committed: https://chromium.googlesource.com/v8/v8/+/e6e968d0e693be75cf68c499a1388ec8c68ccb40

[Devlin, 2017-01-05 17:25:19]

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

[commit-bot: I haz the power, 2017-01-05 17:25:29]

Dry run: 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, 2017-01-05 17:50:36]

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

[commit-bot: I haz the power, 2017-01-05 17:50:37]

Dry run: This issue passed the CQ dry run.

[Devlin, 2017-01-05 17:53:08]

rdevlin.cronin@chromium.org changed reviewers:
+ jochen@chromium.org

[Devlin, 2017-01-05 17:53:08]

jochen@, mind taking a look?  (for reference, I've also started a thread at
https://groups.google.com/a/chromium.org/forum/#!topic/cxx/JbDBw98aeE4 to see if
we should do this far more widely)

[dgozman, 2017-01-07 00:05:02]

dgozman@chromium.org changed reviewers:
+ clemensh@chromium.org, dgozman@chromium.org

[dgozman, 2017-01-07 00:05:03]

Thanks for the fix! lgtm

@clemensh - any objections?

[Clemens Hammacher, 2017-01-07 08:43:31]

Lgtm, thanks!

[jochen (gone - plz use gerrit), 2017-01-09 08:36:39]

lgtm

[Devlin, 2017-01-09 15:50:12]

The CQ bit was checked by rdevlin.cronin@chromium.org

[commit-bot: I haz the power, 2017-01-09 15:50:17]

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, 2017-01-09 16:15:51]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1483977012287180, "parent_rev":
"38602f1ff553b32815d34a05cd6d965f4fc20960", "commit_rev":
"e6e968d0e693be75cf68c499a1388ec8c68ccb40"}

[commit-bot: I haz the power, 2017-01-09 16:15:56]

Description was changed from

==========
Fix String16's move constructor

String16 had a pseudo move constructor that took a const String16&&. The
problem with this is that the point of moving objects is the ability to
clobber the underlying data. If we look at this particular case, the
move ctor tried to then std::move the underlying std::basic_string<>;
this results in passing a const std::basic_string<>&& to the
basic_string ctor. This resolves to the const std::basic_string<>&
*copy* ctor. So in the end, we haven't moved anything.

Fix this by taking a mutable rvalue reference that allows the moving to
work as expected.

BUG=None
==========

to

==========
Fix String16's move constructor

String16 had a pseudo move constructor that took a const String16&&. The
problem with this is that the point of moving objects is the ability to
clobber the underlying data. If we look at this particular case, the
move ctor tried to then std::move the underlying std::basic_string<>;
this results in passing a const std::basic_string<>&& to the
basic_string ctor. This resolves to the const std::basic_string<>&
*copy* ctor. So in the end, we haven't moved anything.

Fix this by taking a mutable rvalue reference that allows the moving to
work as expected.

BUG=None

Review-Url: https://codereview.chromium.org/2616973002
Cr-Commit-Position: refs/heads/master@{#42147}
Committed:
https://chromium.googlesource.com/v8/v8/+/e6e968d0e693be75cf68c499a1388ec8c68...
==========

[commit-bot: I haz the power, 2017-01-09 16:15:57]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/v8/v8/+/e6e968d0e693be75cf68c499a1388ec8c68...