Adding missing #include in send_side_congestion_controller.

Not including <iterator> creates problems on some build systems because
std::back_inserter is defined there.

Bug: None
Change-Id: I27180f72dd327e3a0caab35d3a33907f1e0c4296
Reviewed-on: https://webrtc-review.googlesource.com/69323
Reviewed-by: Sebastian Jansson <srte@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22825}
diff --git a/modules/congestion_controller/send_side_congestion_controller.cc b/modules/congestion_controller/send_side_congestion_controller.cc
index bb959f3..4a17933 100644
--- a/modules/congestion_controller/send_side_congestion_controller.cc
+++ b/modules/congestion_controller/send_side_congestion_controller.cc
@@ -12,6 +12,7 @@
 
 #include <algorithm>
 #include <cstdio>
+#include <iterator>
 #include <memory>
 #include <vector>