Add build targets for Opus tests.

Relanding of Add build targets for Opus tests. (patchset #2 id:20001 of
https://codereview.chromium.org/894473002/)

test_opus_api, test_opus_encode, test_opus_decode, and test_opus_padding
can be run directly, with no command-line options, and they print out
"OK" during the test and an overall status message such as
"All API tests passed." or "Tests completed successfully." at the end.

The celt component has several unit tests. I didn't add build targets
for them because some of them don't print any output, so you'd need a
test harness script to examine their exit status.

R=henrika@chromium.org,sergeyu@chromium.org
BUG=452984
Committed: https://crrev.com/626f929de03b5a32a58c9148970684b890cdca81
Cr-Commit-Position: refs/heads/master@{#314379}

[wtc, 2015-02-03 17:47:08]

A good way to review this relanding CL is to compare it with the original CL
https://codereview.chromium.org/894473002/

The original CL was reverted to make it easier to revert the CL committed before
it.

[Sergey Ulanov, 2015-02-03 17:50:51]

lgtm

[wtc, 2015-02-03 17:57:52]

The CQ bit was checked by wtc@chromium.org

[commit-bot: I haz the power, 2015-02-03 17:58:39]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/891353005/1

[commit-bot: I haz the power, 2015-02-03 19:17:20]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-03 19:18:44]

Patchset 1 (id:??) landed as
https://crrev.com/626f929de03b5a32a58c9148970684b890cdca81
Cr-Commit-Position: refs/heads/master@{#314379}