dbus: Stop accessing ObjectProxy::name_owner_changed_callback_ on the D-Bus thread

dbus: Stop accessing ObjectProxy::name_owner_changed_callback_ on the D-Bus thread

Accessing the callback on the D-Bus thread while changing its value may result in a race condition.
Change the type of SetNameOwnerChangedCallback's argument from Signal to strings to stop worrying about on which thread the Signal gets released.

BUG=298747
TEST=dbus_unittests
R=satorux@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=225675

[satorux1, 2013-09-26 10:41:03]

LGTM. looks a lot simpler!

[commit-bot: I haz the power, 2013-09-26 11:09:34]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/hashimoto@chromium.org/24673006/3001

[commit-bot: I haz the power, 2013-09-26 15:47:32]

Retried try job too often on linux_aura for step(s) browser_tests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=linux_aura...

[commit-bot: I haz the power, 2013-09-27 04:00:41]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/hashimoto@chromium.org/24673006/3001

[commit-bot: I haz the power, 2013-09-27 06:13:49]

Retried try job too often on linux_chromeos for step(s) content_browsertests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=linux_chro...

[commit-bot: I haz the power, 2013-09-27 06:18:42]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/hashimoto@chromium.org/24673006/3001

[hashimoto, 2013-09-27 07:12:33]

Committed patchset #1 manually as r225675 (presubmit successful).