Introduce composed tree version of endOfDocument()

Introduce composed tree version of endOfDocument()

This patch introduces composed tree version of |endOfDocument()| by
templatizing original |endOfDocument()| to work both DOM tree position and
composed tree position version for introducing composed tree version of
|VisibleSelection| class.

This patch is a preparation of making selection to handle granularity for web
component, http://crrev.com/1277863002

BUG=513568
TEST=n/a; no behavior changes

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=201958

[yosin_UTC9, 2015-09-09 05:35:07]

yosin@chromium.org changed reviewers:
+ hajimehoshi@chromium.org, yoichio@chromium.org

[yosin_UTC9, 2015-09-09 05:41:37]

PTAL

[yoichio, 2015-09-09 05:51:15]

lgtm

[yosin_UTC9, 2015-09-09 06:14:35]

The CQ bit was checked by yosin@chromium.org

[commit-bot: I haz the power, 2015-09-09 06:14:43]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1326683006/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1326683006/1

[commit-bot: I haz the power, 2015-09-09 07:23:07]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=201958