Replace NULL with nullptr in all C++ files.

webrtc/test/fake_network_pipe.cc

Index: webrtc/test/fake_network_pipe.cc
diff --git a/webrtc/test/fake_network_pipe.cc b/webrtc/test/fake_network_pipe.cc
index 0b3aa6ac71c2b3695789fb19713d32a0c14ecbc0..e175ca59787a0a31490c411bd1626ddd8f879e77 100644
--- a/webrtc/test/fake_network_pipe.cc
+++ b/webrtc/test/fake_network_pipe.cc
@@ -31,7 +31,7 @@ FakeNetworkPipe::FakeNetworkPipe(Clock* clock,
                                  const FakeNetworkPipe::Config& config,
                                  uint64_t seed)
     : clock_(clock),
-      packet_receiver_(NULL),
+      packet_receiver_(nullptr),
       random_(seed),
       config_(config),
       dropped_packets_(0),
@@ -81,9 +81,9 @@ void FakeNetworkPipe::SetConfig(const FakeNetworkPipe::Config& config) {
 }
 
 void FakeNetworkPipe::SendPacket(const uint8_t* data, size_t data_length) {
-  // A NULL packet_receiver_ means that this pipe will terminate the flow of
+  // A null packet_receiver_ means that this pipe will terminate the flow of
   // packets.
-  if (packet_receiver_ == NULL)
+  if (packet_receiver_ == nullptr)
     return;
   rtc::CritScope crit(&lock_);
   if (config_.queue_length_packets > 0 &&