Added initialization of SessionManagerOperation::slot_.

Added initialization of SessionManagerOperation::slot_.

BUG=377078
TEST=manual
R=mnissler@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=272943

[Mattias Nissler (ping if slow), 2014-05-27 08:48:26]

LGTM

[ygorshenin1, 2014-05-27 08:49:30]

The CQ bit was checked by ygorshenin@chromium.org

[commit-bot: I haz the power, 2014-05-27 08:49:46]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/ygorshenin@chromium.org/297163008/1

[commit-bot: I haz the power, 2014-05-27 10:43:02]

FYI, CQ is re-trying this CL (attempt #1).
Please consider checking whether the failures are real,
and report flakes to chrome-troopers@google.com.
The failing builders are:
  android_aosp on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/android_aosp/builds/7...)

[commit-bot: I haz the power, 2014-05-27 11:08:06]

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

[commit-bot: I haz the power, 2014-05-27 11:08:07]

Try jobs failed on following builders:
  android_aosp on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/android_aosp/builds/7...)

[ygorshenin1, 2014-05-27 11:13:45]

Committed patchset #1 manually as r272943 (presubmit successful).