Ensure that every Document has a single, distinct template content ownerDocument

Ensure that every Document has a single, distinct template content ownerDocument

This avoids several bugs where templates would erroneously share their content
ownerDocuments with themselves, leading to such badness as custom elements being
instantiated inside templates or template.content.ownerDocument.defaultView being
non-null.

Also cleans up various code in Document: templateDocument() is gone, with its callers
switched to the new isTemplateDocument() method, and setTemplateDocumentHost() has
been removed from Document's public interface, since it should only be set by Document
itself.

Spec bug: https://www.w3.org/Bugs/Public/show_bug.cgi?id=23990
Relevant HTML spec change: http://html5.org/tools/web-apps-tracker?from=8350&to=8351

R=rafaelw@chromium.org
BUG=325442, 342601
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=166973

[rafaelw, 2014-02-11 22:28:35]

lgtm

[adamk, 2014-02-11 23:52:32]

The CQ bit was checked by adamk@chromium.org

[adamk, 2014-02-12 00:13:39]

The CQ bit was unchecked by adamk@chromium.org

[adamk, 2014-02-12 00:13:44]

The CQ bit was checked by adamk@chromium.org

[commit-bot: I haz the power, 2014-02-12 02:00:46]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/adamk@chromium.org/159853004/60001

[adamk, 2014-02-12 06:45:06]

The CQ bit was unchecked by adamk@chromium.org

[adamk, 2014-02-12 06:45:12]

The CQ bit was checked by adamk@chromium.org

[commit-bot: I haz the power, 2014-02-12 07:42:04]

Change committed as 166973