Move congestion controller to a separate module.

webrtc/modules/congestion_controller/BUILD.gn

Index: webrtc/modules/congestion_controller/BUILD.gn
diff --git a/webrtc/modules/bitrate_controller/BUILD.gn b/webrtc/modules/congestion_controller/BUILD.gn
similarity index 76%
copy from webrtc/modules/bitrate_controller/BUILD.gn
copy to webrtc/modules/congestion_controller/BUILD.gn
index 5e3741ba933db058e77b5c9434d20ced72aa82cf..8723fe4475300f83190e4c71c434ab366d230118 100644
--- a/webrtc/modules/bitrate_controller/BUILD.gn
+++ b/webrtc/modules/congestion_controller/BUILD.gn
@@ -8,14 +8,10 @@
 
 import("../../build/webrtc.gni")
 
-source_set("bitrate_controller") {
+source_set("congestion_controller") {
   sources = [
-    "bitrate_controller_impl.cc",
-    "bitrate_controller_impl.h",
-    "include/bitrate_allocator.h",
-    "include/bitrate_controller.h",
-    "send_side_bandwidth_estimation.cc",
-    "send_side_bandwidth_estimation.h",
+    "congestion_controller.cc",
+    "include/congestion_controller.h",
   ]
 
   if (is_win) {
@@ -35,6 +31,8 @@ source_set("bitrate_controller") {
   }
 
   deps = [
-    "../../system_wrappers",
+    "../bitrate_controller",
+    "../pacing",
+    "../remote_bitrate_estimator",
   ]
 }