Enable cpplint in pc/

Enable cpplint check in the PRESUBMIT for pc/ and fix all existing
warnings.

Bug: webrtc:5583
Change-Id: If39994692ab6f6f3c83c74f23850f02fdfe810e8
Reviewed-on: https://webrtc-review.googlesource.com/16540
Commit-Queue: Steve Anton <steveanton@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20482}
diff --git a/pc/videotrack.cc b/pc/videotrack.cc
index 718c0d6..bd6d9c2 100644
--- a/pc/videotrack.cc
+++ b/pc/videotrack.cc
@@ -8,11 +8,11 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
+#include <string>
+
 #include "pc/videotrack.h"
 #include "rtc_base/refcountedobject.h"
 
-#include <string>
-
 namespace webrtc {
 
 VideoTrack::VideoTrack(const std::string& label,