Estimating NTP time with a given RTT.

RemoteNtpTimeEstimator needed user to give a remote SSRC and it intended to call RtpRtcp module to obtain RTT, to be able to calculate Ntp time.

When RTT cannot be directly obtained from the RtpRtcp module with the specified SSRC, RemoteNtpTimeEstimator would fail.

This change allows RemoteNtpTimeEstimator to calculate NTP with an external RTT estimate.

An immediate benefit is that capture_start_ntp_time_ms_ can be obtained in a Google hangout call.

BUG=

TEST=chromium + hangout call
R=stefan@webrtc.org, xians@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/24879004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7407 4adac7df-926f-26a2-2b94-8c16560cd09d
Make DEPS find check_root_dir.py in legacy checkouts.

In r7405 the DEPS hook wasn't properly handling the case
when the trunk dir is not yet renamed. This makes the script
only be called if it exists in the old not-yet-renamed trunk dir.

BUG=3534
R=phoglund@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/31639004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7408 4adac7df-926f-26a2-2b94-8c16560cd09d