Allow injection of time controller to NetworkEmulationManagerImpl.

Bug: webrtc:10365
Change-Id: I6a0e04459f75e8134787e605057dcb03cae55cd8
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/132780
Commit-Queue: Sebastian Jansson <srte@webrtc.org>
Reviewed-by: Artem Titov <titovartem@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27631}
diff --git a/test/time_controller/real_time_controller.cc b/test/time_controller/real_time_controller.cc
index 7ad9eef..4e01665 100644
--- a/test/time_controller/real_time_controller.cc
+++ b/test/time_controller/real_time_controller.cc
@@ -38,4 +38,9 @@
   closure();
 }
 
+RealTimeController* GlobalRealTimeController() {
+  static RealTimeController* time_controller = new RealTimeController();
+  return time_controller;
+}
+
 }  // namespace webrtc