Reland: Rename VideoQualityTestFixtureInterface::Params.pipe into config.

Also make it optional and use default value, if optional is not
specified. It is done also for next refactoring, that will introduce
ability to override network simulation layer.

Bug: webrtc:9630
Change-Id: I2f9b84770e428a7738b47bcf2da1002697c0f313
Reviewed-on: https://webrtc-review.googlesource.com/96580
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Commit-Queue: Artem Titov <titovartem@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24472}
diff --git a/video/video_loopback.cc b/video/video_loopback.cc
index 3e7f6b0..52f0a65 100644
--- a/video/video_loopback.cc
+++ b/video/video_loopback.cc
@@ -277,7 +277,7 @@
 }  // namespace flags
 
 void Loopback() {
-  FakeNetworkPipe::Config pipe_config;
+  DefaultNetworkSimulationConfig pipe_config;
   pipe_config.loss_percent = flags::LossPercent();
   pipe_config.avg_burst_loss_length = flags::AvgBurstLossLength();
   pipe_config.link_capacity_kbps = flags::LinkCapacityKbps();
@@ -321,7 +321,7 @@
                      flags::DurationSecs(),
                      flags::OutputFilename(),
                      flags::GraphTitle()};
-  params.pipe = pipe_config;
+  params.config = pipe_config;
 
   if (flags::NumStreams() > 1 && flags::Stream0().empty() &&
       flags::Stream1().empty()) {