Make an AudioEncoder subclass for comfort noise

BUG=3926
R=bjornv@webrtc.org, kjellander@webrtc.org, kwiberg@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/31129004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7857 4adac7df-926f-26a2-2b94-8c16560cd09d
DCHECK: Reference condition parameter in release builds

So that caller's won't get warnings about unused variables for
variables that are only used in calls to DCHECK, such as

  int x = ...
  DCHECK_EQ(x, 17);

R=andrew@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/31169004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7858 4adac7df-926f-26a2-2b94-8c16560cd09d
Revert r7858 ("DCHECK: Reference condition parameter in release builds")

Apparently Visual Studio is cleverer than I am at figuring out what
local variables are actually unused.

TBR=pbos@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/32739004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7859 4adac7df-926f-26a2-2b94-8c16560cd09d
(Auto)update libjingle 81702493-> 81755413

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7860 4adac7df-926f-26a2-2b94-8c16560cd09d