Make VoiceEngine choose ACM2 by default
Make VoiceEngine choose ACM2 by default

The use of a factory for ACM will be removed in later CLs.

BUG=2996
R=henrika@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/12069004

git-svn-id: 917f5d3ca488f358c4d40eaec14422cf392ccec9@5923 4adac7df-926f-26a2-2b94-8c16560cd09d

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