Revert of Revert of Add mechanism to auto mount file systems in response to a URL request.

Revert of Revert of Add mechanism to auto mount file systems in response to a URL request. (https://codereview.chromium.org/206253002/)

Reason for revert:
This revert did not fix the breakage it was suspected of.

Original issue's description:
> Revert of Add mechanism to auto mount file systems in response to a URL request. (https://codereview.chromium.org/195923002/)
> 
> Reason for revert:
> Best guess that this broke
> SyncFileSystemApiTest.WriteFileThenGetUsage
> SyncFileSystemApiTest.GetFileStatuses
> MediaGalleriesPlatformAppBrowserTest.MediaGalleriesCopyTo
> on XP Tests(1).
> 
> Original issue's description:
> > Add mechanism to auto mount file systems in response to a URL request.
> > 
> > This code adds a hook for when a file system URL request can not be cracked.
> > It will allow external media galleries file systems to be lazily created.
> > 
> > BUG=160900
> > 
> > Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=258064
> 
> TBR=kinuko@chromium.org,tzik@chromium.org,joi@chromium.org,sky@chromium.org,vandebo@chromium.org
> NOTREECHECKS=true
> NOTRY=true
> BUG=160900
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=258261

TBR=kinuko@chromium.org,tzik@chromium.org,joi@chromium.org,sky@chromium.org,pneubeck@chromium.org
BUG=160900
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=258440

[vandebo (ex-Chrome), 2014-03-20 16:38:14]

Created Revert of Revert of Add mechanism to auto mount file systems in response
to a URL request.

[vandebo (ex-Chrome), 2014-03-20 16:38:29]

The CQ bit was unchecked by vandebo@chromium.org

[vandebo (ex-Chrome), 2014-03-20 16:38:51]

The CQ bit was checked by vandebo@chromium.org

[commit-bot: I haz the power, 2014-03-20 16:39:44]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/vandebo@chromium.org/199903003/1

[commit-bot: I haz the power, 2014-03-20 17:26:21]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-03-20 17:26:22]

Retried try job too often on win_rel for step(s) app_list_unittests,
ash_unittests, aura_unittests, cacheinvalidation_unittests, cc_unittests,
check_deps, check_deps2git, chrome_elf_unittests, chromedriver_unittests,
components_unittests, compositor_unittests, content_browsertests,
content_unittests, crypto_unittests, events_unittests, gfx_unittests,
google_apis_unittests, gpu_unittests, installer_util_unittests, ipc_tests,
jingle_unittests, media_unittests, mini_installer_test, nacl_integration,
ppapi_unittests, printing_unittests, remoting_unittests, sql_unittests,
sync_integration_tests, sync_unit_tests, telemetry_perf_unittests,
telemetry_unittests, views_unittests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=win_rel&nu...

[vandebo (ex-Chrome), 2014-03-20 17:27:13]

The CQ bit was checked by vandebo@chromium.org

[commit-bot: I haz the power, 2014-03-20 17:29:09]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/vandebo@chromium.org/199903003/1

[commit-bot: I haz the power, 2014-03-20 22:43:57]

Change committed as 258440