Simplify SelfKeepAlive<T>'s representation.

Simplify SelfKeepAlive<T>'s representation.

Following r202197, a Persistent<> is only instantiated when assigned a
non-null pointer value. Consequently, SelfKeepAlive<>'s use of an OwnPtr<>
indirection to achieve the same is no longer needed.

R=haraken
BUG=420515
Committed: https://crrev.com/7054092ea37895921e20bfd5ef4db9caff34a7f7
git-svn-id: svn://svn.chromium.org/blink/trunk@202202 bbb929c8-8fbe-4397-9dbb-9b2b20218538

[sof, 2015-09-14 12:28:50]

sigbjornf@opera.com changed reviewers:
+ oilpan-reviews@chromium.org

[sof, 2015-09-14 12:28:50]

please take a look.

[haraken, 2015-09-14 13:52:46]

LGTM

[sof, 2015-09-14 14:10:09]

The CQ bit was checked by sigbjornf@opera.com

[commit-bot: I haz the power, 2015-09-14 14:10:14]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1339043002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1339043002/1

[commit-bot: I haz the power, 2015-09-14 14:15:31]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=202202

[commit-bot: I haz the power, 2015-09-23 12:32:13]

Patchset 1 (id:??) landed as
https://crrev.com/7054092ea37895921e20bfd5ef4db9caff34a7f7