Verify that constant vectors aren't invalidated during iteration.

Verify that constant vectors aren't invalidated during iteration.

Clearing a heap vector while it is being iterated and on the stack is
unsafe, as it promptly releases the backing store.

Add CHECK()s to verify that this doesn't happen for a crasher involving
MediaQuerySets that's proving hard to pindown, but there are some
suggestions that the heap vector contents of MediaQuerySet::m_queries
is being mutated.

R=
BUG=699269
Review-Url: https://codereview.chromium.org/2806003002
Cr-Commit-Position: refs/heads/master@{#463124}
Committed: https://chromium.googlesource.com/chromium/src/+/b2a0ce3e8a9b3e561c67cf0a2772c4567567b9f6

[sof, 2017-04-07 20:32:36]

The CQ bit was checked by sigbjornf@opera.com to run a CQ dry run

[commit-bot: I haz the power, 2017-04-07 20:33:35]

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

[sof, 2017-04-07 20:52:45]

sigbjornf@opera.com changed reviewers:
+ haraken@chromium.org, meade@chromium.org

[sof, 2017-04-07 20:52:46]

please take a look.

i can't explain all MediaQuerySet-related crash stacks from a bug like this, but
worth verifying at this stage that we're not mutating the vectors while
iterating.

[haraken, 2017-04-07 22:38:05]

LGTM

(I was chatting with keishi@ about MediaQuery crashes yesterday but didn't come
up with any idea. This CL is definitely interesting :-)

[commit-bot: I haz the power, 2017-04-07 22:57:03]

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

[commit-bot: I haz the power, 2017-04-07 22:57:04]

Dry run: This issue passed the CQ dry run.

[sof, 2017-04-08 05:15:21]

The CQ bit was checked by sigbjornf@opera.com

[commit-bot: I haz the power, 2017-04-08 05:15:35]

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, 2017-04-08 05:19:20]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1491628521977340, "parent_rev":
"b7a39ee8b67804ad9aee3fda6510608b7aa319d0", "commit_rev":
"b2a0ce3e8a9b3e561c67cf0a2772c4567567b9f6"}

[commit-bot: I haz the power, 2017-04-08 05:20:14]

Description was changed from

==========
Verify that constant vectors aren't invalidated during iteration.

Clearing a heap vector while it is being iterated and on the stack is
unsafe, as it promptly releases the backing store.

Add CHECK()s to verify that this doesn't happen for a crasher involving
MediaQuerySets that's proving hard to pindown, but there are some
suggestions that the heap vector contents of MediaQuerySet::m_queries
is being mutated.

R=
BUG=699269
==========

to

==========
Verify that constant vectors aren't invalidated during iteration.

Clearing a heap vector while it is being iterated and on the stack is
unsafe, as it promptly releases the backing store.

Add CHECK()s to verify that this doesn't happen for a crasher involving
MediaQuerySets that's proving hard to pindown, but there are some
suggestions that the heap vector contents of MediaQuerySet::m_queries
is being mutated.

R=
BUG=699269

Review-Url: https://codereview.chromium.org/2806003002
Cr-Commit-Position: refs/heads/master@{#463124}
Committed:
https://chromium.googlesource.com/chromium/src/+/b2a0ce3e8a9b3e561c67cf0a2772...
==========

[commit-bot: I haz the power, 2017-04-08 05:20:15]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/chromium/src/+/b2a0ce3e8a9b3e561c67cf0a2772...