Set up SSRCs correctly after switching codec.

Before SSRCs were not set up correctly, as the old VideoEngine API
doesn't support setting additional SSRCs before a codec with as many
streams are set.

No test was in place to catch this, so two tests are added to make sure
that we send the SSRCs that are set, and also that we can switch from
using one to using all SSRCs, even though initially not all of them are
set up.

BUG=
R=mflodman@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/4539004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@5188 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/test/rtp_rtcp_observer.h

@@ -43,7 +43,9 @@ class RtpRtcpObserver {
   }
 
   virtual EventTypeWrapper Wait() {
-    return observation_complete_->Wait(timeout_ms_);
+    EventTypeWrapper result = observation_complete_->Wait(timeout_ms_);
+    observation_complete_->Reset();
+    return result;
   }
 
  protected: