Fix cpplint errors in p2p/

Bug: webrtc:5273
Change-Id: Ida3c2ca1bbb611026f34d7144db9ec24840bf7fb
Reviewed-on: https://webrtc-review.googlesource.com/26444
Commit-Queue: Steve Anton <steveanton@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21133}
diff --git a/p2p/base/stunrequest.cc b/p2p/base/stunrequest.cc
index 15ee24b..851bd70 100644
--- a/p2p/base/stunrequest.cc
+++ b/p2p/base/stunrequest.cc
@@ -12,6 +12,7 @@
 
 #include <algorithm>
 #include <memory>
+#include <vector>
 
 #include "rtc_base/checks.h"
 #include "rtc_base/helpers.h"