Delay Estimator: Adds unittests for robust validation.

In addition to unittests a cast losing constness was corrected.
The tests added are:
1. Adjusting allowed_offset when robust validation is disabled should have no impact.
2. For noise free signals there should be no difference between robust validation or not.
3. Robust validation acts faster during startup.

BUG=None
TESTED=modules_unittests, trybots
R=aluebs@webrtc.org, andrew@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/6789004

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@5361 4adac7df-926f-26a2-2b94-8c16560cd09d
2 files changed