[fsp] [recommit] Add FileSystemURLParser to the file system provider.

[fsp] [recommit] Add FileSystemURLParser to the file system provider.

The FileSystemURLParser is a class which parses a cracked FileSystemURL to
associate it with the proper ProvidedFileSystem class handling this URL.

This will be necessary to route operations from AsyncFileUtil to a proper
providing extension.

Along the way, the Service class has been fixed. Now, the provided file systems
are gracefully unmounted in destructor. As a result, the external mount points
are cleared neatly.

Previously reverted, because depending on a CL to be reverted.
See: https://codereview.chromium.org/237583015

TBR=kinaba@chromium.org
TEST=unit_tests: FileSystemProviderMountPathUtilTest*
BUG=248427
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=264975

[mtomasz, 2014-04-21 04:15:47]

@kinaba: TBR. This is the same as https://codereview.chromium.org/237583015, but
with a rebase. This CL got reverted before, but only because it was depending on
a bad CL.

[mtomasz, 2014-04-21 04:15:51]

The CQ bit was checked by mtomasz@chromium.org

[commit-bot: I haz the power, 2014-04-21 04:15:56]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/mtomasz@chromium.org/244623003/1

[commit-bot: I haz the power, 2014-04-21 04:15:57]

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

[commit-bot: I haz the power, 2014-04-21 04:15:57]

No LGTM from a valid reviewer yet. Only full committers are accepted.
Even if an LGTM may have been provided, it was from a non-committer or
a lowly provisional committer, _not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.

[kinaba, 2014-04-21 04:17:45]

lgtm

[mtomasz, 2014-04-21 04:17:49]

The CQ bit was checked by mtomasz@chromium.org

[commit-bot: I haz the power, 2014-04-21 04:17:56]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/mtomasz@chromium.org/244623003/1

[commit-bot: I haz the power, 2014-04-21 05:49:42]

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

[commit-bot: I haz the power, 2014-04-21 05:49:42]

Try jobs failed on following builders:
  tryserver.chromium on mac_chromium_rel

[mtomasz, 2014-04-21 07:18:33]

The CQ bit was checked by mtomasz@chromium.org

[commit-bot: I haz the power, 2014-04-21 07:18:40]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/mtomasz@chromium.org/244623003/20001

[commit-bot: I haz the power, 2014-04-21 10:37:05]

Change committed as 264975