Make WebPageSerializerImpl to escape URL attribute values in result.

Make WebPageSerializerImpl to escape URL attribute values in result.

This patch makes |WebPageSerializerImpl| to escape URL attribute values rather
than directly output URL attribute values into result.

BUG=542054
TEST=webkit_unit_tests --gtest_filter=WebPageSerializerTest.URLAttributeValues

Committed: https://crrev.com/b770d85e37b2d0e248f04cf20606a2f3871ef039
Cr-Commit-Position: refs/heads/master@{#353712}

[yosin_UTC9, 2015-10-13 08:54:52]

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

[yosin_UTC9, 2015-10-13 08:55:44]

PTAL

This patch fixes a security bug.

[tkent, 2015-10-13 08:59:07]

lgtm

[yosin_UTC9, 2015-10-13 09:01:21]

The CQ bit was checked by yosin@chromium.org

[yosin_UTC9, 2015-10-13 09:01:22]

The patchset sent to the CQ was uploaded after l-g-t-m from tkent@chromium.org
Link to the patchset: https://codereview.chromium.org/1398453005/#ps20001
(title: "2015-10-13T17:56:56 Rebase")

[commit-bot: I haz the power, 2015-10-13 09:01:30]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1398453005/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1398453005/20001

[commit-bot: I haz the power, 2015-10-13 10:00:28]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-10-13 10:01:17]

Patchset 2 (id:??) landed as
https://crrev.com/b770d85e37b2d0e248f04cf20606a2f3871ef039
Cr-Commit-Position: refs/heads/master@{#353712}