Change ShowConfirmBubble() to take model by scoped_ptr.

Change ShowConfirmBubble() to take model by scoped_ptr.

It makes the ownership clear and it is a good pratice when transfering
ownership from caller to callee. Passing a scoped_ptr makes it harder to
misuse.

Discussion in chromium-dev mailing-list:
https://groups.google.com/a/chromium.org/d/topic/chromium-dev/9rTsfEI1Ux0/discussion

BUG=None
TEST=unit_tests --gtest_filter=ConfirmBubble*
R=pkasting@chromium.org,avi@chromium.org

Committed: https://crrev.com/f19a75afa37614c9e13af2b9a462d00377b9e57b
Cr-Commit-Position: refs/heads/master@{#308292}

[tfarina, 2014-12-12 23:45:03]

PTAL

[Peter Kasting, 2014-12-12 23:47:23]

LGTM

[Avi (use Gerrit), 2014-12-13 03:41:46]

lgtm

Yes! I like it.

[tfarina, 2014-12-14 01:32:37]

The CQ bit was checked by tfarina@chromium.org

[commit-bot: I haz the power, 2014-12-14 01:33:28]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/801043003/1

[commit-bot: I haz the power, 2014-12-14 02:19:08]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-12-14 02:20:03]

Patchset 1 (id:??) landed as
https://crrev.com/f19a75afa37614c9e13af2b9a462d00377b9e57b
Cr-Commit-Position: refs/heads/master@{#308292}