Pull the Voice Activity Detector out from the AGC

Pull the Voice Activity Detector out from the AGC

This change generates bit-exact values when running through audioproc_f than before.

This change was originally uploaded here:
* https://codereview.webrtc.org/1181933002/
* https://codereview.webrtc.org/1177043017/

And reverted because of an ASAN problem in Chrome here:
* https://codereview.webrtc.org/1192863006/
* https://codereview.webrtc.org/1194963003/

TBR=andrew@webrtc.org

Committed: https://crrev.com/518c683f3e413523a458a94b533274bd7f29992d
Cr-Commit-Position: refs/heads/master@{#9502}

[aluebs-webrtc, 2015-06-25 01:02:42]

The CQ bit was checked by aluebs@webrtc.org

[commit-bot: I haz the power, 2015-06-25 01:02:58]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1211563003/1

[commit-bot: I haz the power, 2015-06-25 01:46:01]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-25 01:46:10]

Patchset 1 (id:??) landed as
https://crrev.com/518c683f3e413523a458a94b533274bd7f29992d
Cr-Commit-Position: refs/heads/master@{#9502}