Use MountGuest to mount cryptohome for a demo user.

Use MountGuest to mount cryptohome for a demo user.
Doing a regular user mount with the ephemeral flag doesn't work very well since cryptohome expects the machine to either have an owner or be enterprise owned for normal user mounts, even if ephemeral. This CL switches us to using the mount guest path in cryptohome.
This involves changing the path followed by LoginUtils::PrepareProfile since there are multiple things that it does that we either do not want, or cannot have, for a guest mount.

Additionally, we cannot MountGuest with our normal demo mode user_id since Cryptohome (and a few other cros components) expect the username for a guest mount to be $guest. To get around this, we mount crytohome with $guest as the username, but once the mount is done, we switch the username back to the demo user name for the rest of the processsing being done in Chrome.

R=dpolukhin@chromium.org, xiyuan@chromium.org
BUG=345038
TEST=Tested on a device on OOBE with the TPM cleared.

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=252193

[Dmitry Polukhin, 2014-02-20 00:02:47]

lgtm

https://codereview.chromium.org/171423009/diff/40001/chrome/browser/chromeos/...
File chrome/browser/chromeos/app_mode/kiosk_profile_loader.cc (right):

https://codereview.chromium.org/171423009/diff/40001/chrome/browser/chromeos/...
chrome/browser/chromeos/app_mode/kiosk_profile_loader.cc:154: if
(context.username == UserManager::kGuestUserName)
Please add comment why you do this substitution.

[rkc, 2014-02-20 00:05:38]

https://codereview.chromium.org/171423009/diff/40001/chrome/browser/chromeos/...
File chrome/browser/chromeos/app_mode/kiosk_profile_loader.cc (right):

https://codereview.chromium.org/171423009/diff/40001/chrome/browser/chromeos/...
chrome/browser/chromeos/app_mode/kiosk_profile_loader.cc:154: if
(context.username == UserManager::kGuestUserName)
On 2014/02/20 00:02:48, Dmitry Polukhin wrote:
> Please add comment why you do this substitution.

Done.

[rkc, 2014-02-20 00:05:54]

The CQ bit was checked by rkc@chromium.org

[rkc, 2014-02-20 01:20:49]

The CQ bit was unchecked by rkc@chromium.org

[commit-bot: I haz the power, 2014-02-20 01:20:56]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/rkc@chromium.org/171423009/70001

[rkc, 2014-02-20 01:20:56]

The CQ bit was checked by rkc@chromium.org

[rkc, 2014-02-20 04:49:33]

The CQ bit was checked by rkc@chromium.org

[rkc, 2014-02-20 05:55:53]

The CQ bit was unchecked by rkc@chromium.org

[rkc, 2014-02-20 05:56:27]

The CQ bit was checked by rkc@chromium.org

[rkc, 2014-02-20 05:58:40]

The CQ bit was unchecked by rkc@chromium.org

[rkc, 2014-02-20 08:57:16]

Committed patchset #3 manually as r252193 (presubmit successful).

[Nikita (slow), 2014-06-10 16:48:44]

I'm currently doing refactoring in this area and was actually unifying these two
paths.

https://codereview.chromium.org/171423009/diff/70001/chrome/browser/chromeos/...
File chrome/browser/chromeos/login/login_utils.cc (right):

https://codereview.chromium.org/171423009/diff/70001/chrome/browser/chromeos/...
chrome/browser/chromeos/login/login_utils.cc:430:
ProfileManager::GetGuestProfilePath(),
Are you sure that this is actually working?

All other parts of Chrome OS are not using Guest Profile.

In this case profile is supposed to be at /home/chronos/Guest Profile but
Cryptohome doesn't know about that and mounts tmps to

/home/chronos/u-[$guest hash]
(or legacy one /home/chronos/user).

[Nikita (slow), 2014-06-10 17:47:48]

On 2014/06/10 16:48:44, Nikita Kostylev wrote:
> I'm currently doing refactoring in this area and was actually unifying these
two
> paths.

Here's CL in progress https://codereview.chromium.org/318853004/

[Nikita (slow), 2014-06-11 09:44:40]

https://codereview.chromium.org/171423009/diff/70001/chrome/browser/chromeos/...
File chrome/browser/chromeos/login/login_utils.cc (right):

https://codereview.chromium.org/171423009/diff/70001/chrome/browser/chromeos/...
chrome/browser/chromeos/login/login_utils.cc:430:
ProfileManager::GetGuestProfilePath(),
On 2014/06/10 16:48:43, Nikita Kostylev wrote:
> Are you sure that this is actually working?
> 
> All other parts of Chrome OS are not using Guest Profile.
> 
> In this case profile is supposed to be at /home/chronos/Guest Profile but
> Cryptohome doesn't know about that and mounts tmps to
> 
> /home/chronos/u-[$guest hash]
> (or legacy one /home/chronos/user).

So I've actually found that this issue was fixed right away in
https://codereview.chromium.org/205713002

Sorry for the noise.