VideoSendStreamTest.SwapsI420VideoFrames: Initialize frame memory to avoid drmemory errors
VideoSendStreamTest.SwapsI420VideoFrames: Initialize frame memory to avoid drmemory errors

R=pbos@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/27149004

git-svn-id: 03ae4fbe531b1eefc9d815f31e49022782c42458@7688 4adac7df-926f-26a2-2b94-8c16560cd09d

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