Enable cpplint in media/

Bug: webrtc:5584
Change-Id: I2fd1395d35596d9002e19cc90fcda3a5d4cde9e7
Reviewed-on: https://webrtc-review.googlesource.com/16564
Commit-Queue: Steve Anton <steveanton@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20504}
diff --git a/media/engine/webrtcvideoencoderfactory.h b/media/engine/webrtcvideoencoderfactory.h
index 53a529a..97ac03b 100644
--- a/media/engine/webrtcvideoencoderfactory.h
+++ b/media/engine/webrtcvideoencoderfactory.h
@@ -11,6 +11,7 @@
 #ifndef MEDIA_ENGINE_WEBRTCVIDEOENCODERFACTORY_H_
 #define MEDIA_ENGINE_WEBRTCVIDEOENCODERFACTORY_H_
 
+#include <string>
 #include <vector>
 
 #include "common_types.h"  // NOLINT(build/include)