Probing: Add support for exponential startup probing

Adds support for exponentially probing the bandwidth at start-up to allow
ramp-up to real capacity of the network.

BUG=webrtc:6332
R=philipel@webrtc.org, stefan@webrtc.org

Review URL: https://codereview.webrtc.org/2235373004 .

Cr-Commit-Position: refs/heads/master@{#14189}
diff --git a/webrtc/modules/congestion_controller/congestion_controller_unittest.cc b/webrtc/modules/congestion_controller/congestion_controller_unittest.cc
index 53ccf3d..79cb2ed 100644
--- a/webrtc/modules/congestion_controller/congestion_controller_unittest.cc
+++ b/webrtc/modules/congestion_controller/congestion_controller_unittest.cc
@@ -12,6 +12,7 @@
 #include "testing/gtest/include/gtest/gtest.h"
 #include "webrtc/call/mock/mock_rtc_event_log.h"
 #include "webrtc/modules/pacing/mock/mock_paced_sender.h"
+#include "webrtc/modules/bitrate_controller/include/bitrate_controller.h"
 #include "webrtc/modules/congestion_controller/include/congestion_controller.h"
 #include "webrtc/modules/congestion_controller/include/mock/mock_congestion_controller.h"
 #include "webrtc/modules/remote_bitrate_estimator/include/mock/mock_remote_bitrate_observer.h"