Change jingle_unittests target to a test executable.

Change jingle_unittests target to a test executable.

Everything seems to link now.

Tested with the following command lines:

$ gn gen out-gn
$ ninja -C out-gn/ jingle_unittests
$ out-gn/jingle_unittests

This fixes one more TODO(GYP).

BUG=None
TEST=see above
R=sergeyu@chromium.org

Committed: https://crrev.com/1b1006ac316595d0a849a167816d46e8fb01177b
Cr-Commit-Position: refs/heads/master@{#317045}

[Sergey Ulanov, 2015-02-19 05:02:28]

lgtm

[tfarina, 2015-02-19 14:43:25]

The CQ bit was checked by tfarina@chromium.org

[commit-bot: I haz the power, 2015-02-19 14:43:44]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/929433006/1

[commit-bot: I haz the power, 2015-02-19 14:46:39]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-19 14:47:16]

Patchset 1 (id:??) landed as
https://crrev.com/1b1006ac316595d0a849a167816d46e8fb01177b
Cr-Commit-Position: refs/heads/master@{#317045}