Minor tweak to Session* to use base::Passed so ownership is clearer

Minor tweak to Session* to use base::Passed so ownership is clearer

BUG=none
TEST=none
R=skuhne@chromium.org

Committed: https://crrev.com/4883738595d0dde983244f921dd0d336312971f2
Cr-Commit-Position: refs/heads/master@{#302335}

[Mr4D (OOO till 08-26), 2014-10-31 17:58:30]

lgtm

[sky, 2014-10-31 17:59:14]

The CQ bit was checked by sky@chromium.org

[commit-bot: I haz the power, 2014-10-31 18:00:29]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/689143002/1

[commit-bot: I haz the power, 2014-10-31 18:24:19]

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

[commit-bot: I haz the power, 2014-10-31 18:24:19]

Try jobs failed on following builders:
  linux_chromium_rel_ng on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)
  win8_chromium_rel on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win8_chromium_rel...)
  win_chromium_rel_ng on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_rel_...)

[sky, 2014-10-31 20:31:14]

The CQ bit was checked by sky@chromium.org

[commit-bot: I haz the power, 2014-10-31 20:32:07]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/689143002/20001

[commit-bot: I haz the power, 2014-10-31 22:12:06]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2014-10-31 22:12:49]

Patchset 2 (id:??) landed as
https://crrev.com/4883738595d0dde983244f921dd0d336312971f2
Cr-Commit-Position: refs/heads/master@{#302335}