mojo: Fix leveldb unittests by making fs::Directories cloneable.

mojo: Fix leveldb unittests by making fs::Directories cloneable.

This adds a Clone() method to mojo filesystem Directory objects, along
with making it safe to clone Directory objects that represent temporary
directories so that the temporary directory sticks around as long as
there's a single open File or Directory referencing it.

Using this, we can fix the last flaky LevelDBServiceTest that needed to
access the filesystem.

BUG=602820
Committed: https://crrev.com/a95c3cd937908671730b1b8aad013492b7670796
Cr-Commit-Position: refs/heads/master@{#391040}

[Elliot Glaysher, 2016-05-02 17:27:13]

erg@chromium.org changed reviewers:
+ jam@chromium.org

[jam, 2016-05-02 19:04:15]

lgtm

[Elliot Glaysher, 2016-05-02 19:05:16]

The CQ bit was checked by erg@chromium.org

[commit-bot: I haz the power, 2016-05-02 19:05:29]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1935863002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1935863002/20001

[commit-bot: I haz the power, 2016-05-02 20:13:54]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2016-05-02 20:15:13]

Description was changed from

==========
mojo: Fix leveldb unittests by making fs::Directories cloneable.

This adds a Clone() method to mojo filesystem Directory objects, along
with making it safe to clone Directory objects that represent temporary
directories so that the temporary directory sticks around as long as
there's a single open File or Directory referencing it.

Using this, we can fix the last flaky LevelDBServiceTest that needed to
access the filesystem.

BUG=602820
==========

to

==========
mojo: Fix leveldb unittests by making fs::Directories cloneable.

This adds a Clone() method to mojo filesystem Directory objects, along
with making it safe to clone Directory objects that represent temporary
directories so that the temporary directory sticks around as long as
there's a single open File or Directory referencing it.

Using this, we can fix the last flaky LevelDBServiceTest that needed to
access the filesystem.

BUG=602820

Committed: https://crrev.com/a95c3cd937908671730b1b8aad013492b7670796
Cr-Commit-Position: refs/heads/master@{#391040}
==========

[commit-bot: I haz the power, 2016-05-02 20:15:14]

Patchset 2 (id:??) landed as
https://crrev.com/a95c3cd937908671730b1b8aad013492b7670796
Cr-Commit-Position: refs/heads/master@{#391040}