Revert of Revert of Inline sign in extracts gaia id from HTTP header and seeds account tracker

Revert of Revert of Inline sign in extracts gaia id from HTTP header and seeds account tracker (patchset #1 id:1 of https://codereview.chromium.org/671183002/)

Reason for revert:
White success page and no way to proceed only reproduces for use_athena=1 builds.

This CL fixes that: https://codereview.chromium.org/642693003/

Re-landing.

Original issue's description:
> Revert of Inline sign in extracts gaia id from HTTP header and seeds account tracker (patchset #46 id:1740001 of https://codereview.chromium.org/473153002/)
>
> Reason for revert:
> This breaks Chrome OS GAIA login.
>
> After successful GAIA authentication uses sees blank white page and nothing happens.
>
> Please build chromeos=1 build and check that sign in as new user works fine before relanding this CL. Unfortunately autotests rely on fake gaia server and doesn't check this end-to-end sign in flow.
>
> Original issue's description:
> > Inline login handler extracts gaia id from HTTP header and seeds account tracker
> > service during sign in.
> >
> > BUG=341408
> >
> > Committed: https://crrev.com/a8e7c94b1b79a0948d05a1fcfff53391d22ce37a
> > Cr-Commit-Position: refs/heads/master@{#300750}
>
> TBR=guohui@chromium.org,bartfab@chromium.org,xiyuan@chromium.org,achuith@chromium.org,davemoore@chromium.org,rogerta@chromium.org
> NOTREECHECKS=true
> NOTRY=true
> BUG=341408
>
> Committed: https://crrev.com/bbaf207927765f4b7c7cae2a4af8db6c4c4a67ce
> Cr-Commit-Position: refs/heads/master@{#300873}

TBR=guohui@chromium.org,bartfab@chromium.org,xiyuan@chromium.org,achuith@chromium.org,davemoore@chromium.org,rogerta@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=341408
Committed: https://crrev.com/07398a38454635dcbebac7898cbaa91969741e60
Cr-Commit-Position: refs/heads/master@{#301099}

[Nikita (slow), 2014-10-24 14:34:29]

Created Revert of Revert of Inline sign in extracts gaia id from HTTP header and
seeds account tracker

[commit-bot: I haz the power, 2014-10-24 14:35:13]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/677703002/1

[commit-bot: I haz the power, 2014-10-24 14:36:11]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-10-24 14:36:55]

Patchset 1 (id:??) landed as
https://crrev.com/07398a38454635dcbebac7898cbaa91969741e60
Cr-Commit-Position: refs/heads/master@{#301099}

[bartfab (slow), 2014-10-27 14:32:18]

lgtm