easy-signin: Wire GetSignInChallenge.

easy-signin: Wire GetSignInChallenge.

- Fetch crypthome keys when EasyUnlockServiceSignIn is assocated with a user;
- Translate and provide remote devices and challenge from key data;

BUG=401636
Committed: https://crrev.com/048cedfbcda51787df4674c96ad2bd534aff9941
Cr-Commit-Position: refs/heads/master@{#295610}

[xiyuan, 2014-09-18 00:19:10]

xiyuan@chromium.org changed reviewers:
+ tbarzic@chromium.org, tengs@chromium.org

[xiyuan, 2014-09-18 00:20:35]

Not ready for review yet. Just a heads up. Will ping back when I tested it and
ready.

[xiyuan, 2014-09-18 21:04:33]

Manually tested it by hard coding a user name on service initialize and use dev
tools to call getSignInChallenge.

Please review and comment. Thanks.

[tbarzic, 2014-09-18 21:12:18]

lgtm

[xiyuan, 2014-09-18 23:14:24]

The CQ bit was checked by xiyuan@chromium.org

[commit-bot: I haz the power, 2014-09-18 23:16:31]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/576383002/20001

[commit-bot: I haz the power, 2014-09-18 23:49:30]

Committed patchset #2 (id:20001) as e1e90ad08a0cc585e151469999dbae54ad4ef997

[commit-bot: I haz the power, 2014-09-18 23:50:08]

Patchset 2 (id:??) landed as
https://crrev.com/048cedfbcda51787df4674c96ad2bd534aff9941
Cr-Commit-Position: refs/heads/master@{#295610}