Replace NULL with nullptr in all C++ files.

webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl_unittest.cc

Index: webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl_unittest.cc
diff --git a/webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl_unittest.cc b/webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl_unittest.cc
index ae4aad7c8412112f25e942cf67416608290ae3d0..4e1010782f0e2d181cc4f9fba9a1adf9613d01eb 100644
--- a/webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl_unittest.cc
+++ b/webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl_unittest.cc
@@ -53,11 +53,10 @@ class SendTransport : public Transport,
                       public NullRtpData {
  public:
   SendTransport()
-      : receiver_(NULL),
-        clock_(NULL),
+      : receiver_(nullptr),
+        clock_(nullptr),
         delay_ms_(0),
-        rtp_packets_sent_(0) {
-  }
+        rtp_packets_sent_(0) {}
 
   void SetRtpRtcpModule(ModuleRtpRtcpImpl* receiver) {
     receiver_ = receiver;