Switch "Downloads" directory path to the per-profile ones for multi-profile support.

Switch "Downloads" directory path to the per-profile ones for multi-profile support.

All migration code has already landed. This is the final CL that carries out the switch.
By this CL, Files.app in multi-profile session starts showing each profile's Downloads folder,
not the primary profile's one. This is a transient state for the future fully-multiprofile-aware
Files.app (ETA: M34) that shows all profile's folder in a single window.

The following is the summary/background why the path switch is needed:

We had used /home/chronos/user/Download as the path to the "Downloads" folder for all users.
This does not hold for multi-profile session. The "real" path for multiple users are
/home/chronos/u-unique-hash-userA/Downloads
/home/chronos/u-unique-hash-userB/Downloads
...
and /home/chronos/user is just an alias to the user who first signed into the session.

To make all user's folder available simultaneously in one multi-profile session,
we need to stop using the alias, and differentiate all folders by the real path.

BUG=309556
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=243794

[hirono, 2014-01-09 04:08:07]

lgtm!

[commit-bot: I haz the power, 2014-01-09 05:38:51]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/kinaba@chromium.org/48903012/130001

[commit-bot: I haz the power, 2014-01-09 07:31:07]

Change committed as 243794