Enable file_system_provider::Service in incognito.

Enable file_system_provider::Service in incognito.

There is no need to limit the FSP API to non-incognito only. Especially, such
limitation was causing crashes in Files app running in incognito, which
assumed the service exists, but it didn't.

With this CL the service is created for both non-incognito and incognito pages.
Both instances are *same*, so mounted providers will be shared between incognito
and non-incognito windows.

TEST=Tested manually by launching with --incognito
BUG=487901
Committed: https://crrev.com/5c23b37e51dba88729571ad01360c7ffc40737d5
Cr-Commit-Position: refs/heads/master@{#329792}

[mtomasz, 2015-05-14 02:00:36]

Patchset #2 (id:20001) has been deleted

[mtomasz, 2015-05-14 02:02:10]

mtomasz@chromium.org changed reviewers:
+ hirono@chromium.org

[mtomasz, 2015-05-14 02:02:24]

@hirono: PTAL. Thanks.

[hirono, 2015-05-14 03:29:00]

lgtm

[mtomasz, 2015-05-14 03:29:58]

The CQ bit was checked by mtomasz@chromium.org

[commit-bot: I haz the power, 2015-05-14 03:30:29]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1138423002/1

[commit-bot: I haz the power, 2015-05-14 03:33:58]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-05-14 03:34:40]

Patchset 1 (id:??) landed as
https://crrev.com/5c23b37e51dba88729571ad01360c7ffc40737d5
Cr-Commit-Position: refs/heads/master@{#329792}