Move a member function parentEditingBoundary() out from PositionAlgorithm<Strategy> template class

Move a member function parentEditingBoundary() out from PositionAlgorithm<Strategy> template class

This patch moves a member function |parentEditingBoundary()| in
|PositionAlgorithm<Strategy>| template class for a preparation of making it
as static function in "VisibileUnits.cpp" since it is used only in
"VisibileUnits.cpp".

BUG=518738
TEST=n/a; no behavior changes

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=200827

[yosin_UTC9, 2015-08-19 05:43:35]

PTAL

[yosin_UTC9, 2015-08-19 06:32:18]

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

[yosin_UTC9, 2015-08-19 06:32:18]

PTAL

[hajimehoshi, 2015-08-19 08:10:06]

lgtm

[yosin_UTC9, 2015-08-19 08:33:00]

The CQ bit was checked by yosin@chromium.org

[commit-bot: I haz the power, 2015-08-19 08:33:05]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1298233004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1298233004/1

[commit-bot: I haz the power, 2015-08-19 08:34:19]

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

[commit-bot: I haz the power, 2015-08-19 08:34:20]

Try jobs failed on following builders:
  linux_chromium_compile_dbg_32_ng on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)
  mac_chromium_compile_dbg_ng on tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_comp...)

[yosin_UTC9, 2015-08-19 13:28:36]

Patchset #2 (id:20001) has been deleted

[yosin_UTC9, 2015-08-19 13:31:32]

Patchset #2 (id:40001) has been deleted

[yosin_UTC9, 2015-08-19 13:32:04]

The CQ bit was checked by yosin@chromium.org

[yosin_UTC9, 2015-08-19 13:32:05]

The patchset sent to the CQ was uploaded after l-g-t-m from
hajimehoshi@chromium.org
Link to the patchset: https://codereview.chromium.org/1298233004/#ps60001
(title: "2015-08-19T22:31:05 Rebase")

[commit-bot: I haz the power, 2015-08-19 13:32:11]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1298233004/60001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1298233004/60001

[commit-bot: I haz the power, 2015-08-19 14:37:03]

Committed patchset #2 (id:60001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=200827