arc: Send cryptohome ID on starting ARC instance.

arc: Send cryptohome ID on starting ARC instance.

We are soon moving android-data directory from the current
fixed path (/home/chronos/user/android-data) to a path inside
mounted cryptohome (/home/root/<CryptohomeID>/android-data).
To prepare for that change, we start sending cryptohome ID in
StartArcInstance() D-Bus method.

Since we do not use |socket_path| parameter at all in
session_manager today, we will reuse it to pass the cryptohome ID.

BUG=b:26700652
TEST=trybot
TEST=ARC boots

Committed: https://crrev.com/73ba2139159c3225e9d0f28d6066fac07b4fe80a
Cr-Commit-Position: refs/heads/master@{#398232}

[Shuhei Takahashi, 2016-05-30 11:13:03]

nya@chromium.org changed reviewers:
+ dspaid@chromium.org, hashimoto@chromium.org, lhchavez@chromium.org,
oshima@chromium.org

[Shuhei Takahashi, 2016-05-30 11:13:04]

hashimoto: PTAL chromeos/

oshima: PTAL chrome/

lhchavez: PTAL all

dspaid: FYI (let's chat offline tomorrow)

[hashimoto, 2016-05-30 11:20:17]

https://codereview.chromium.org/2023803003/diff/1/chromeos/dbus/session_manag...
File chromeos/dbus/session_manager_client.h (right):

https://codereview.chromium.org/2023803003/diff/1/chromeos/dbus/session_manag...
chromeos/dbus/session_manager_client.h:217: // socket for communication with the
instance.  Upon completion, invokes
Please add a comment about cryptohome_id.

[Shuhei Takahashi, 2016-05-30 11:47:51]

https://codereview.chromium.org/2023803003/diff/1/chromeos/dbus/session_manag...
File chromeos/dbus/session_manager_client.h (right):

https://codereview.chromium.org/2023803003/diff/1/chromeos/dbus/session_manag...
chromeos/dbus/session_manager_client.h:217: // socket for communication with the
instance.  Upon completion, invokes
On 2016/05/30 11:20:17, hashimoto wrote:
> Please add a comment about cryptohome_id.

Done.

[hashimoto, 2016-05-30 11:49:54]

chromeos/dbus lgtm

[Luis Héctor Chávez, 2016-05-31 15:35:23]

hmmm that was supposed to be the role of the |socket_path| parameter. Can't you
use that?

If you cannot use that, it's probably better to remove |socket_path| since it's
redundant.

[Shuhei Takahashi, 2016-05-31 16:54:51]

On 2016/05/31 15:35:23, Luis Héctor Chávez wrote:
> hmmm that was supposed to be the role of the |socket_path| parameter. Can't
you
> use that?
> 
> If you cannot use that, it's probably better to remove |socket_path| since
it's
> redundant.

IIUC |socket_path| is always a fixed path "/var/run/chrome/arc_bridge.sock". It
does not contain any user-id-specific path components.

https://code.google.com/p/chromium/codesearch#chromium/src/components/arc/arc...

What do you mean by "that was supposed to be the role of the |socket_path|
parameter"?

[Luis Héctor Chávez, 2016-05-31 16:58:33]

On 2016/05/31 16:54:51, Shuhei Takahashi wrote:
> On 2016/05/31 15:35:23, Luis Héctor Chávez wrote:
> > hmmm that was supposed to be the role of the |socket_path| parameter. Can't
> you
> > use that?
> > 
> > If you cannot use that, it's probably better to remove |socket_path| since
> it's
> > redundant.
> 
> IIUC |socket_path| is always a fixed path "/var/run/chrome/arc_bridge.sock".
It
> does not contain any user-id-specific path components.
> 
>
https://code.google.com/p/chromium/codesearch#chromium/src/components/arc/arc...
> 
> What do you mean by "that was supposed to be the role of the |socket_path|
> parameter"?

At some point it was supposed to be in the data directory. But then it wasn't,
so now it's just passing over a constant.

As it stands it's unneeded to pass in both parameters, only one is needed.

[Shuhei Takahashi, 2016-05-31 17:36:57]

On 2016/05/31 16:58:33, Luis Héctor Chávez wrote:
> On 2016/05/31 16:54:51, Shuhei Takahashi wrote:
> > On 2016/05/31 15:35:23, Luis Héctor Chávez wrote:
> > > hmmm that was supposed to be the role of the |socket_path| parameter.
Can't
> > you
> > > use that?
> > > 
> > > If you cannot use that, it's probably better to remove |socket_path| since
> > it's
> > > redundant.
> > 
> > IIUC |socket_path| is always a fixed path "/var/run/chrome/arc_bridge.sock".
> It
> > does not contain any user-id-specific path components.
> > 
> >
>
https://code.google.com/p/chromium/codesearch#chromium/src/components/arc/arc...
> > 
> > What do you mean by "that was supposed to be the role of the |socket_path|
> > parameter"?
> 
> At some point it was supposed to be in the data directory. But then it wasn't,
> so now it's just passing over a constant.
> 
> As it stands it's unneeded to pass in both parameters, only one is needed.

I see your point. However we can't deprecate |socket_path| immediately in this
change because we need several preparation steps to move socket path.

I think a rough plan would be:

1. Submit this change as-is (i.e. do nothing with |socket_path|).
2. Modify Chrome to create socket under /home/root/$hash. |socket_path| starts
to point the new path, but session_manager still uses it to locate socket.
3. Modify session_manager to construct socket path from |cryptohome_id|, not
from |socket_path|.
4. Modify Chrome to send nothing in |socket_path| to deprecate the parameter (or
if you know any good way to remove a parameter from D-bus method please let me
know).

Let me find or create a bug entry to track this issue tomorrow.

[Luis Héctor Chávez, 2016-05-31 17:55:55]

On 2016/05/31 17:36:57, Shuhei Takahashi wrote:
> On 2016/05/31 16:58:33, Luis Héctor Chávez wrote:
> > On 2016/05/31 16:54:51, Shuhei Takahashi wrote:
> > > On 2016/05/31 15:35:23, Luis Héctor Chávez wrote:
> > > > hmmm that was supposed to be the role of the |socket_path| parameter.
> Can't
> > > you
> > > > use that?
> > > > 
> > > > If you cannot use that, it's probably better to remove |socket_path|
since
> > > it's
> > > > redundant.
> > > 
> > > IIUC |socket_path| is always a fixed path
"/var/run/chrome/arc_bridge.sock".
> > It
> > > does not contain any user-id-specific path components.
> > > 
> > >
> >
>
https://code.google.com/p/chromium/codesearch#chromium/src/components/arc/arc...
> > > 
> > > What do you mean by "that was supposed to be the role of the |socket_path|
> > > parameter"?
> > 
> > At some point it was supposed to be in the data directory. But then it
wasn't,
> > so now it's just passing over a constant.
> > 
> > As it stands it's unneeded to pass in both parameters, only one is needed.
> 
> I see your point. However we can't deprecate |socket_path| immediately in this
> change because we need several preparation steps to move socket path.
> 
> I think a rough plan would be:
> 
> 1. Submit this change as-is (i.e. do nothing with |socket_path|).
> 2. Modify Chrome to create socket under /home/root/$hash. |socket_path| starts
> to point the new path, but session_manager still uses it to locate socket.

This is not *strictly* needed, since session_manager doesn't even use this
parameter :P And there are no plans to use it in the future.

> 3. Modify session_manager to construct socket path from |cryptohome_id|, not
> from |socket_path|.
> 4. Modify Chrome to send nothing in |socket_path| to deprecate the parameter
(or
> if you know any good way to remove a parameter from D-bus method please let me
> know).
> 
> Let me find or create a bug entry to track this issue tomorrow.

How about the following alternative: given that it's more painful to modify dbus
messages without having them break (since they are just read linearly), just
replace |socket_path| with |cryptohome_id| or the fully-built path to
/home/user/$hash/ if we don't need to build /home/root/$hash/ as well. It's
going to be marshaled as a string anyways and you won't need to do any
deprecation steps. You will only need to change session_manager+dbus bindings
once to rename the parameter, but that change can happen separately since the
parameter name is not needed and is only for documentation.

[Shuhei Takahashi, 2016-05-31 18:04:09]

On 2016/05/31 17:55:55, Luis Héctor Chávez wrote:
> On 2016/05/31 17:36:57, Shuhei Takahashi wrote:
> > On 2016/05/31 16:58:33, Luis Héctor Chávez wrote:
> > > On 2016/05/31 16:54:51, Shuhei Takahashi wrote:
> > > > On 2016/05/31 15:35:23, Luis Héctor Chávez wrote:
> > > > > hmmm that was supposed to be the role of the |socket_path| parameter.
> > Can't
> > > > you
> > > > > use that?
> > > > > 
> > > > > If you cannot use that, it's probably better to remove |socket_path|
> since
> > > > it's
> > > > > redundant.
> > > > 
> > > > IIUC |socket_path| is always a fixed path
> "/var/run/chrome/arc_bridge.sock".
> > > It
> > > > does not contain any user-id-specific path components.
> > > > 
> > > >
> > >
> >
>
https://code.google.com/p/chromium/codesearch#chromium/src/components/arc/arc...
> > > > 
> > > > What do you mean by "that was supposed to be the role of the
|socket_path|
> > > > parameter"?
> > > 
> > > At some point it was supposed to be in the data directory. But then it
> wasn't,
> > > so now it's just passing over a constant.
> > > 
> > > As it stands it's unneeded to pass in both parameters, only one is needed.
> > 
> > I see your point. However we can't deprecate |socket_path| immediately in
this
> > change because we need several preparation steps to move socket path.
> > 
> > I think a rough plan would be:
> > 
> > 1. Submit this change as-is (i.e. do nothing with |socket_path|).
> > 2. Modify Chrome to create socket under /home/root/$hash. |socket_path|
starts
> > to point the new path, but session_manager still uses it to locate socket.
> 
> This is not *strictly* needed, since session_manager doesn't even use this
> parameter :P And there are no plans to use it in the future.
> 
> > 3. Modify session_manager to construct socket path from |cryptohome_id|, not
> > from |socket_path|.
> > 4. Modify Chrome to send nothing in |socket_path| to deprecate the parameter
> (or
> > if you know any good way to remove a parameter from D-bus method please let
me
> > know).
> > 
> > Let me find or create a bug entry to track this issue tomorrow.
> 
> How about the following alternative: given that it's more painful to modify
dbus
> messages without having them break (since they are just read linearly), just
> replace |socket_path| with |cryptohome_id| or the fully-built path to
> /home/user/$hash/ if we don't need to build /home/root/$hash/ as well. It's
> going to be marshaled as a string anyways and you won't need to do any
> deprecation steps. You will only need to change session_manager+dbus bindings
> once to rename the parameter, but that change can happen separately since the
> parameter name is not needed and is only for documentation.

Oh I did not notice that |socket_path| is not used in session_manager :)

Your suggestion to replace |socket_path| with |cryptohome_id| sounds good. I'll
revise the patch tomorrow. Thanks!

[oshima, 2016-05-31 21:32:56]

On 2016/05/31 18:04:09, Shuhei Takahashi wrote:
> On 2016/05/31 17:55:55, Luis Héctor Chávez wrote:
> > On 2016/05/31 17:36:57, Shuhei Takahashi wrote:
> > > On 2016/05/31 16:58:33, Luis Héctor Chávez wrote:
> > > > On 2016/05/31 16:54:51, Shuhei Takahashi wrote:
> > > > > On 2016/05/31 15:35:23, Luis Héctor Chávez wrote:
> > > > > > hmmm that was supposed to be the role of the |socket_path|
parameter.
> > > Can't
> > > > > you
> > > > > > use that?
> > > > > > 
> > > > > > If you cannot use that, it's probably better to remove |socket_path|
> > since
> > > > > it's
> > > > > > redundant.
> > > > > 
> > > > > IIUC |socket_path| is always a fixed path
> > "/var/run/chrome/arc_bridge.sock".
> > > > It
> > > > > does not contain any user-id-specific path components.
> > > > > 
> > > > >
> > > >
> > >
> >
>
https://code.google.com/p/chromium/codesearch#chromium/src/components/arc/arc...
> > > > > 
> > > > > What do you mean by "that was supposed to be the role of the
> |socket_path|
> > > > > parameter"?
> > > > 
> > > > At some point it was supposed to be in the data directory. But then it
> > wasn't,
> > > > so now it's just passing over a constant.
> > > > 
> > > > As it stands it's unneeded to pass in both parameters, only one is
needed.
> > > 
> > > I see your point. However we can't deprecate |socket_path| immediately in
> this
> > > change because we need several preparation steps to move socket path.
> > > 
> > > I think a rough plan would be:
> > > 
> > > 1. Submit this change as-is (i.e. do nothing with |socket_path|).
> > > 2. Modify Chrome to create socket under /home/root/$hash. |socket_path|
> starts
> > > to point the new path, but session_manager still uses it to locate socket.
> > 
> > This is not *strictly* needed, since session_manager doesn't even use this
> > parameter :P And there are no plans to use it in the future.
> > 
> > > 3. Modify session_manager to construct socket path from |cryptohome_id|,
not
> > > from |socket_path|.
> > > 4. Modify Chrome to send nothing in |socket_path| to deprecate the
parameter
> > (or
> > > if you know any good way to remove a parameter from D-bus method please
let
> me
> > > know).
> > > 
> > > Let me find or create a bug entry to track this issue tomorrow.
> > 
> > How about the following alternative: given that it's more painful to modify
> dbus
> > messages without having them break (since they are just read linearly), just
> > replace |socket_path| with |cryptohome_id| or the fully-built path to
> > /home/user/$hash/ if we don't need to build /home/root/$hash/ as well. It's
> > going to be marshaled as a string anyways and you won't need to do any
> > deprecation steps. You will only need to change session_manager+dbus
bindings
> > once to rename the parameter, but that change can happen separately since
the
> > parameter name is not needed and is only for documentation.
> 
> Oh I did not notice that |socket_path| is not used in session_manager :)
> 
> Your suggestion to replace |socket_path| with |cryptohome_id| sounds good.
I'll
> revise the patch tomorrow. Thanks!

holding my review based on the discussion.

[Shuhei Takahashi, 2016-06-01 01:54:15]

nya@chromium.org changed reviewers:
+ dzhioev@chromium.org

[Shuhei Takahashi, 2016-06-01 01:54:15]

dzhioev: PTAL for DEPS to user_manager

others: PTAL again


As per discussion with Luis, I've replaced unused |socket_path| with
|cryptohome_id|.

[Shuhei Takahashi, 2016-06-01 01:56:02]

Description was changed from

==========
arc: Send account ID on starting ARC instance.

We are soon moving android-data directory from the current
fixed path (/home/chronos/user/android-data) to a path
containing username hash. To prepare for that change, we start
sending account ID in StartArcInstance() D-Bus method.

BUG=b:26700652
TEST=trybot
TEST=ARC boots
==========

to

==========
arc: Send account ID on starting ARC instance.

We are soon moving android-data directory from the current
fixed path (/home/chronos/user/android-data) to a path
containing username hash. To prepare for that change, we start
sending account ID in StartArcInstance() D-Bus method.

Since we do not use |socket_path| parameter at all in
session_manager today, we will reuse it to pass the account ID.

BUG=b:26700652
TEST=trybot
TEST=ARC boots
==========

[oshima, 2016-06-01 02:10:23]

lgtm with nit

https://codereview.chromium.org/2023803003/diff/40001/chromeos/dbus/session_m...
File chromeos/dbus/session_manager_client.h (right):

https://codereview.chromium.org/2023803003/diff/40001/chromeos/dbus/session_m...
chromeos/dbus/session_manager_client.h:219: virtual void StartArcInstance(const
cryptohome::Identification& cryptohome_id,
Some description about failure case would be helpful.

[hashimoto, 2016-06-01 03:45:26]

chromeos/dbus lgtm

[Shuhei Takahashi, 2016-06-01 05:24:58]

https://codereview.chromium.org/2023803003/diff/40001/chromeos/dbus/session_m...
File chromeos/dbus/session_manager_client.h (right):

https://codereview.chromium.org/2023803003/diff/40001/chromeos/dbus/session_m...
chromeos/dbus/session_manager_client.h:219: virtual void StartArcInstance(const
cryptohome::Identification& cryptohome_id,
On 2016/06/01 02:10:23, oshima wrote:
> Some description about failure case would be helpful.

Actually it turned out this function does not check dbus error except for
no-such-method... Please let me fix it and add comments in another change.

[Luis Héctor Chávez, 2016-06-01 15:36:45]

lgtm much better :)

[Shuhei Takahashi, 2016-06-02 08:24:31]

dzhioev:

I'm now wondering if user_manager->GetActiveUser() really gives what we want.
IIUC "active user" is the user whose desktop is currently being shown, but then
what if this code path is executed when multiple users are logged in to the
device?

[Shuhei Takahashi, 2016-06-02 08:47:54]

lhchavez: PTAL again for arc_bridge_bootstrap.cc

dzhioev: PTAL


On 2016/06/02 08:24:31, Shuhei Takahashi wrote:
> dzhioev:
> 
> I'm now wondering if user_manager->GetActiveUser() really gives what we want.
> IIUC "active user" is the user whose desktop is currently being shown, but
then
> what if this code path is executed when multiple users are logged in to the
> device?

It turned the primary user is what we want. Revised the patch.

[Luis Héctor Chávez, 2016-06-02 15:44:21]

slgtm

[Shuhei Takahashi, 2016-06-06 10:25:38]

dzhioev: ping?

[Shuhei Takahashi, 2016-06-07 02:55:01]

nya@chromium.org changed reviewers:
+ alemate@chromium.org

[Shuhei Takahashi, 2016-06-07 02:55:02]

+alemate: PTAL for user_manager DEPS

I tried to contact dzhioev but got no response.

[Alexander Alekseev, 2016-06-07 03:05:02]

not lgtm.
Need to discuss.

[Shuhei Takahashi, 2016-06-07 03:37:57]

Description was changed from

==========
arc: Send account ID on starting ARC instance.

We are soon moving android-data directory from the current
fixed path (/home/chronos/user/android-data) to a path
containing username hash. To prepare for that change, we start
sending account ID in StartArcInstance() D-Bus method.

Since we do not use |socket_path| parameter at all in
session_manager today, we will reuse it to pass the account ID.

BUG=b:26700652
TEST=trybot
TEST=ARC boots
==========

to

==========
arc: Send cryptohome ID on starting ARC instance.

We are soon moving android-data directory from the current
fixed path (/home/chronos/user/android-data) to
/home/root/<CID>/android-data. To prepare for that change,
we start sending cryptohome ID in StartArcInstance() D-Bus
method.

Since we do not use |socket_path| parameter at all in
session_manager today, we will reuse it to pass the cryptohome ID.

BUG=b:26700652
TEST=trybot
TEST=ARC boots
==========

[Shuhei Takahashi, 2016-06-07 03:38:40]

Description was changed from

==========
arc: Send cryptohome ID on starting ARC instance.

We are soon moving android-data directory from the current
fixed path (/home/chronos/user/android-data) to
/home/root/<CID>/android-data. To prepare for that change,
we start sending cryptohome ID in StartArcInstance() D-Bus
method.

Since we do not use |socket_path| parameter at all in
session_manager today, we will reuse it to pass the cryptohome ID.

BUG=b:26700652
TEST=trybot
TEST=ARC boots
==========

to

==========
arc: Send cryptohome ID on starting ARC instance.

We are soon moving android-data directory from the current
fixed path (/home/chronos/user/android-data) to a path inside
mounted cryptohome (/home/root/<CID>/android-data).
To prepare for that change, we start sending cryptohome ID in
StartArcInstance() D-Bus method.

Since we do not use |socket_path| parameter at all in
session_manager today, we will reuse it to pass the cryptohome ID.

BUG=b:26700652
TEST=trybot
TEST=ARC boots
==========

[Shuhei Takahashi, 2016-06-07 03:40:05]

Description was changed from

==========
arc: Send cryptohome ID on starting ARC instance.

We are soon moving android-data directory from the current
fixed path (/home/chronos/user/android-data) to a path inside
mounted cryptohome (/home/root/<CID>/android-data).
To prepare for that change, we start sending cryptohome ID in
StartArcInstance() D-Bus method.

Since we do not use |socket_path| parameter at all in
session_manager today, we will reuse it to pass the cryptohome ID.

BUG=b:26700652
TEST=trybot
TEST=ARC boots
==========

to

==========
arc: Send cryptohome ID on starting ARC instance.

We are soon moving android-data directory from the current
fixed path (/home/chronos/user/android-data) to a path inside
mounted cryptohome (/home/root/<CryptohomeID>/android-data).
To prepare for that change, we start sending cryptohome ID in
StartArcInstance() D-Bus method.

Since we do not use |socket_path| parameter at all in
session_manager today, we will reuse it to pass the cryptohome ID.

BUG=b:26700652
TEST=trybot
TEST=ARC boots
==========

[Alexander Alekseev, 2016-06-07 03:42:51]

lgtm.

THank you for updating Cl description.

[Shuhei Takahashi, 2016-06-07 04:05:44]

The CQ bit was checked by nya@chromium.org

[Shuhei Takahashi, 2016-06-07 04:05:44]

The patchset sent to the CQ was uploaded after l-g-t-m from
hashimoto@chromium.org, lhchavez@chromium.org, oshima@chromium.org
Link to the patchset: https://codereview.chromium.org/2023803003/#ps60001
(title: "s/GetActiveUser/GetPrimaryUser/g")

[commit-bot: I haz the power, 2016-06-07 04:06:02]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/2023803003/60001

[commit-bot: I haz the power, 2016-06-07 05:21:38]

Description was changed from

==========
arc: Send cryptohome ID on starting ARC instance.

We are soon moving android-data directory from the current
fixed path (/home/chronos/user/android-data) to a path inside
mounted cryptohome (/home/root/<CryptohomeID>/android-data).
To prepare for that change, we start sending cryptohome ID in
StartArcInstance() D-Bus method.

Since we do not use |socket_path| parameter at all in
session_manager today, we will reuse it to pass the cryptohome ID.

BUG=b:26700652
TEST=trybot
TEST=ARC boots
==========

to

==========
arc: Send cryptohome ID on starting ARC instance.

We are soon moving android-data directory from the current
fixed path (/home/chronos/user/android-data) to a path inside
mounted cryptohome (/home/root/<CryptohomeID>/android-data).
To prepare for that change, we start sending cryptohome ID in
StartArcInstance() D-Bus method.

Since we do not use |socket_path| parameter at all in
session_manager today, we will reuse it to pass the cryptohome ID.

BUG=b:26700652
TEST=trybot
TEST=ARC boots
==========

[commit-bot: I haz the power, 2016-06-07 05:21:40]

Committed patchset #4 (id:60001)

[commit-bot: I haz the power, 2016-06-07 05:23:21]

Description was changed from

==========
arc: Send cryptohome ID on starting ARC instance.

We are soon moving android-data directory from the current
fixed path (/home/chronos/user/android-data) to a path inside
mounted cryptohome (/home/root/<CryptohomeID>/android-data).
To prepare for that change, we start sending cryptohome ID in
StartArcInstance() D-Bus method.

Since we do not use |socket_path| parameter at all in
session_manager today, we will reuse it to pass the cryptohome ID.

BUG=b:26700652
TEST=trybot
TEST=ARC boots
==========

to

==========
arc: Send cryptohome ID on starting ARC instance.

We are soon moving android-data directory from the current
fixed path (/home/chronos/user/android-data) to a path inside
mounted cryptohome (/home/root/<CryptohomeID>/android-data).
To prepare for that change, we start sending cryptohome ID in
StartArcInstance() D-Bus method.

Since we do not use |socket_path| parameter at all in
session_manager today, we will reuse it to pass the cryptohome ID.

BUG=b:26700652
TEST=trybot
TEST=ARC boots

Committed: https://crrev.com/73ba2139159c3225e9d0f28d6066fac07b4fe80a
Cr-Commit-Position: refs/heads/master@{#398232}
==========

[commit-bot: I haz the power, 2016-06-07 05:23:22]

Patchset 4 (id:??) landed as
https://crrev.com/73ba2139159c3225e9d0f28d6066fac07b4fe80a
Cr-Commit-Position: refs/heads/master@{#398232}

[Shuhei Takahashi, 2016-06-09 05:26:19]

Description was changed from

==========
arc: Send cryptohome ID on starting ARC instance.

We are soon moving android-data directory from the current
fixed path (/home/chronos/user/android-data) to a path inside
mounted cryptohome (/home/root/<CryptohomeID>/android-data).
To prepare for that change, we start sending cryptohome ID in
StartArcInstance() D-Bus method.

Since we do not use |socket_path| parameter at all in
session_manager today, we will reuse it to pass the cryptohome ID.

BUG=b:26700652
TEST=trybot
TEST=ARC boots

Committed: https://crrev.com/73ba2139159c3225e9d0f28d6066fac07b4fe80a
Cr-Commit-Position: refs/heads/master@{#398232}
==========

to

==========
arc: Send cryptohome ID on starting ARC instance.

We are soon moving android-data directory from the current
fixed path (/home/chronos/user/android-data) to a path inside
mounted cryptohome (/home/root/<CryptohomeID>/android-data).
To prepare for that change, we start sending cryptohome ID in
StartArcInstance() D-Bus method.

Since we do not use |socket_path| parameter at all in
session_manager today, we will reuse it to pass the cryptohome ID.

BUG=b:26700652
TEST=trybot
TEST=ARC boots

Committed: https://crrev.com/73ba2139159c3225e9d0f28d6066fac07b4fe80a
Cr-Commit-Position: refs/heads/master@{#398232}
==========