Add ramp-up tests for transport sequence number with and w/o audio.

Also add a perf metric tracking the average network latency.

The audio stream test is disabled for now since audio isn't included in bitrate allocation.

BUG=webrtc:5263
R=mflodman@webrtc.org

Review URL: https://codereview.webrtc.org/1582833002 .

Cr-Commit-Position: refs/heads/master@{#11244}
diff --git a/webrtc/test/direct_transport.cc b/webrtc/test/direct_transport.cc
index 6f7f998..591e154 100644
--- a/webrtc/test/direct_transport.cc
+++ b/webrtc/test/direct_transport.cc
@@ -70,6 +70,10 @@
   return true;
 }
 
+int DirectTransport::GetAverageDelayMs() {
+  return fake_network_.AverageDelay();
+}
+
 bool DirectTransport::NetworkProcess(void* transport) {
   return static_cast<DirectTransport*>(transport)->SendPackets();
 }