Move AudioDecoderPcm16B next to AudioEncoderPcm16B

Move AudioDecoderPcm16B next to AudioEncoderPcm16B

All AudioDecoder subclasses have historically lived in NetEq, but they
fit better with the codec they wrap.

BUG=webrtc:4557
R=henrik.lundin@webrtc.org

Committed: https://crrev.com/c0ac6cad00f51b99fafaa7c19e2e63b3b542735b
Cr-Commit-Position: refs/heads/master@{#9963}

[kwiberg-webrtc, 2015-09-16 12:46:43]

kwiberg@webrtc.org changed reviewers:
+ henrik.lundin@webrtc.org

[kwiberg-webrtc, 2015-09-16 12:48:01]

As noted elsewhere, this CL leads to the AudioDecoder subclass not being
excluded from the build when it should be, just as is already the case with the
AudioEncoder subclass and the codec's C implementation. I'll deal with that
problem all at once in a future CL.

[hlundin-webrtc, 2015-09-16 12:52:16]

lgtm

[kwiberg-webrtc, 2015-09-17 05:44:47]

The CQ bit was checked by kwiberg@webrtc.org

[kwiberg-webrtc, 2015-09-17 05:44:47]

The patchset sent to the CQ was uploaded after l-g-t-m from
henrik.lundin@webrtc.org
Link to the patchset: https://codereview.webrtc.org/1348113002/#ps40001 (title:
"rebase")

[commit-bot: I haz the power, 2015-09-17 05:44:59]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1348113002/40001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1348113002/40001

[commit-bot: I haz the power, 2015-09-17 05:46:43]

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

[commit-bot: I haz the power, 2015-09-17 05:46:44]

Try jobs failed on following builders:
  presubmit on tryserver.webrtc (JOB_FAILED,
http://build.chromium.org/p/tryserver.webrtc/builders/presubmit/builds/796)

[kwiberg-webrtc, 2015-09-17 05:48:01]

Committed patchset #3 (id:40001) manually as
c0ac6cad00f51b99fafaa7c19e2e63b3b542735b (presubmit successful).

[commit-bot: I haz the power, 2015-09-17 05:48:07]

Patchset 3 (id:??) landed as
https://crrev.com/c0ac6cad00f51b99fafaa7c19e2e63b3b542735b
Cr-Commit-Position: refs/heads/master@{#9963}