Relanding of "Adding BitrateController to audio network adaptor."

Adding BitrateController to audio network adaptor was first landed in https://codereview.webrtc.org/2334613002/ but reverted in https://codereview.webrtc.org/2352223002/ due to ODR violation.

This CL tries to use namespace trick to solve the ODR problem.

BUG=webrtc:6303

Review-Url: https://codereview.webrtc.org/2353293002
Cr-Commit-Position: refs/heads/master@{#14343}
diff --git a/webrtc/modules/audio_coding/audio_network_adaptor/audio_network_adaptor_impl_unittest.cc b/webrtc/modules/audio_coding/audio_network_adaptor/audio_network_adaptor_impl_unittest.cc
index c17d389..6562674 100644
--- a/webrtc/modules/audio_coding/audio_network_adaptor/audio_network_adaptor_impl_unittest.cc
+++ b/webrtc/modules/audio_coding/audio_network_adaptor/audio_network_adaptor_impl_unittest.cc
@@ -28,6 +28,7 @@
 
 MATCHER_P(NetworkMetricsIs, metric, "") {
   return arg.uplink_bandwidth_bps == metric.uplink_bandwidth_bps &&
+         arg.target_audio_bitrate_bps == metric.target_audio_bitrate_bps &&
          arg.uplink_packet_loss_fraction == metric.uplink_packet_loss_fraction;
 }