Use PathService to get temp dir name for IPC unittests.

Use PathService to get temp dir name for IPC unittests.

1) Use PathService() instead of hard-coded "/var/tmp" to get temp dir name.
2) Remove socket files at the end of unittests if it is created by NAMED_SERVER mode.

These unittests fail for Chromecast.

BUG=

Committed: https://crrev.com/e2295ebec1d8c0acfb66672a6dada93fd342ad9d
Cr-Commit-Position: refs/heads/master@{#312635}

[byungchul, 2015-01-21 22:40:18]

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

[byungchul, 2015-01-22 01:54:53]

byungchul@chromium.org changed reviewers:
+ agl@chromium.org, tsepez@chromium.org

[jam, 2015-01-22 16:48:04]

jam@chromium.org changed reviewers:
- jam@chromium.org

[jam, 2015-01-22 16:48:05]

you don't need 3 reviewers for this, i'm removing myself.

[Tom Sepez, 2015-01-22 17:36:37]

I think this is OK even though we will now be getting a path of /tmp instead of
/var/tmp on some platforms.  LGTM.

[byungchul, 2015-01-22 17:38:11]

The CQ bit was checked by byungchul@chromium.org

[commit-bot: I haz the power, 2015-01-22 17:40:07]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/862823003/20001

[commit-bot: I haz the power, 2015-01-22 17:44:28]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-01-22 17:45:18]

Patchset 2 (id:??) landed as
https://crrev.com/e2295ebec1d8c0acfb66672a6dada93fd342ad9d
Cr-Commit-Position: refs/heads/master@{#312635}