Sync: fix crash in DeviceInfoDataTypeController::Subscription destructor.

Sync: fix crash in DeviceInfoDataTypeController::Subscription destructor.

There are reports of crashes in DeviceInfoDataTypeController destructor. The
crash occurs when DeviceInfoDataTypeController has a pending subscription to
LocalDeviceInfoProvider and LocalDeviceInfoProvider gets destroyed first. This
doesn't happen normally as the subscription gets cleared once
LocalDeviceInfoProvider finishes its initialization.

The fix is to clear subscription in StopModel overrides in the two classes that
hold DeviceInfoDataTypeController::Subscription.

BUG=426205
Committed: https://crrev.com/71fcc6c0d1ca865879da48c85b94e4c35f5a378a
Cr-Commit-Position: refs/heads/master@{#301053}

[stanisc, 2014-10-23 16:45:50]

stanisc@chromium.org changed reviewers:
+ pavely@chromium.org

[stanisc, 2014-10-23 16:45:51]

Please review. The fix is fairly small.

[pavely, 2014-10-23 22:56:34]

Did you consider moving local_device_ above directory_data_type_controllers_ in
ProfileSyncService? This would guarantee correct destruction order without
introducing gentlemen's agreement that certain functions will be called.

[stanisc, 2014-10-23 23:51:36]

On 2014/10/23 22:56:34, pavely wrote:
> Did you consider moving local_device_ above directory_data_type_controllers_
in
> ProfileSyncService? This would guarantee correct destruction order without
> introducing gentlemen's agreement that certain functions will be called.

I thought about that but directory_data_type_controllers_ map values are
refcounted so theoretically DeviceInfoDataTypeController could still outlive
local_device_.

[pavely, 2014-10-24 00:07:30]

lgtm

[stanisc, 2014-10-24 04:08:32]

The CQ bit was checked by stanisc@chromium.org

[commit-bot: I haz the power, 2014-10-24 04:09:47]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/672863002/1

[commit-bot: I haz the power, 2014-10-24 05:11:41]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-10-24 05:13:09]

Patchset 1 (id:??) landed as
https://crrev.com/71fcc6c0d1ca865879da48c85b94e4c35f5a378a
Cr-Commit-Position: refs/heads/master@{#301053}