Avoid WTF::Vector::at() and operator[] in core/xml.

Avoid WTF::Vector::at() and operator[] in core/xml.

at() and operator[] are slow due to RELEASE_ASSERT. We can avoid the slowness by
range-based |for|.

This CL has no behavior changes except runtime performance.

BUG=668300
Committed: https://crrev.com/c02417a9281de18ce956313d8b893a328c85f605
Cr-Commit-Position: refs/heads/master@{#437202}

[tkent, 2016-12-08 01:14:57]

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

[commit-bot: I haz the power, 2016-12-08 01:15:35]

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, 2016-12-08 02:45:30]

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

[commit-bot: I haz the power, 2016-12-08 02:45:30]

Dry run: This issue passed the CQ dry run.

[tkent, 2016-12-08 03:07:00]

tkent@chromium.org changed reviewers:
+ hayato@chromium.org

[tkent, 2016-12-08 03:07:01]

hayato@, would you review this please?

[hayato, 2016-12-08 06:56:00]

lgtm

[tkent, 2016-12-08 07:02:55]

The CQ bit was checked by tkent@chromium.org

[commit-bot: I haz the power, 2016-12-08 07:03:13]

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, 2016-12-08 07:08:33]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1481180575013130, "parent_rev":
"bf477be21856022b76589cd265ffe46600510f2a", "commit_rev":
"851e12a1413fc90218fa5b59102485909f12a981"}

[commit-bot: I haz the power, 2016-12-08 07:09:00]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-12-08 07:11:47]

Description was changed from

==========
Avoid WTF::Vector::at() and operator[] in core/xml.

at() and operator[] are slow due to RELEASE_ASSERT. We can avoid the slowness by
range-based |for|.

This CL has no behavior changes except runtime performance.

BUG=668300
==========

to

==========
Avoid WTF::Vector::at() and operator[] in core/xml.

at() and operator[] are slow due to RELEASE_ASSERT. We can avoid the slowness by
range-based |for|.

This CL has no behavior changes except runtime performance.

BUG=668300

Committed: https://crrev.com/c02417a9281de18ce956313d8b893a328c85f605
Cr-Commit-Position: refs/heads/master@{#437202}
==========

[commit-bot: I haz the power, 2016-12-08 07:11:48]

Patchset 1 (id:??) landed as
https://crrev.com/c02417a9281de18ce956313d8b893a328c85f605
Cr-Commit-Position: refs/heads/master@{#437202}