The webrtc::AudioFrame struct contains a variable energy_. Since the energy isn't always calculated when the frame is created, this change makes the CalculateEnergy method in Audio Conference Mixer always calculate the energy.

This part of the the aftermath of issue 3255.

BUG=3255
R=andrew@webrtc.org, henrike@webrtc.org, turaj@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/16479004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@6117 4adac7df-926f-26a2-2b94-8c16560cd09d