WebPrivatePtr: avoid creating temporary Persistent<> on assignment.

WebPrivatePtr: avoid creating temporary Persistent<> on assignment.

For RefCountedGarbageCollected objects wrapped in a WebPrivatePtr, the
PtrStorageImpl::assign(PassRefPtr<T>) overload potentially created a
Persistent on assigning its underlying raw pointer, even if a RawPtr<>
was passed along (due to the implicit RawPtr<T> conversion that
PassRefPtr<T> provides.)

This assign() overload serves no real purpose with Oilpan enabled;
provide a more appropriate RawPtr<T> version there.

R=haraken@chromium.org,tkent@chromium.org
BUG=357163
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=175558

[sof, 2014-06-05 07:54:54]

Please take a look.

[haraken, 2014-06-05 07:58:35]

LGTM

[tkent, 2014-06-05 08:00:00]

lgtm

[sof, 2014-06-05 08:05:23]

The CQ bit was checked by sigbjornf@opera.com

[commit-bot: I haz the power, 2014-06-05 08:06:18]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/sigbjornf@opera.com/313173009/40001

[commit-bot: I haz the power, 2014-06-05 09:15:37]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  mac_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/mac_blink_rel/builds/10394)

[commit-bot: I haz the power, 2014-06-05 10:12:26]

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

[commit-bot: I haz the power, 2014-06-05 10:12:26]

Try jobs failed on following builders:
  mac_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/mac_blink_rel/builds/10406)

[sof, 2014-06-05 10:35:40]

The CQ bit was checked by sigbjornf@opera.com

[commit-bot: I haz the power, 2014-06-05 10:36:19]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/sigbjornf@opera.com/313173009/40001

[commit-bot: I haz the power, 2014-06-05 11:28:37]

Change committed as 175558