Using a right-sided (absolute value), truncated gaussian distribution originally with zero mean.
Currently truncated at x = 3 * std_dev.
Added expected value computation.
Modified jitter unittests accordingly.
BUG=webrtc:4848
R=stefan@webrtc.org
Review URL: https://codereview.webrtc.org/1237303002 .
Cr-Commit-Position: refs/heads/master@{#9587}