Replace NULL with nullptr in all C++ files.

webrtc/modules/video_coding/codecs/test/packet_manipulator.cc

Index: webrtc/modules/video_coding/codecs/test/packet_manipulator.cc
diff --git a/webrtc/modules/video_coding/codecs/test/packet_manipulator.cc b/webrtc/modules/video_coding/codecs/test/packet_manipulator.cc
index b554b4e9aec50307a7305959af7a5253d8f78d85..84e5fc9a66d6c0647cbe36c648b5830e6affffad 100644
--- a/webrtc/modules/video_coding/codecs/test/packet_manipulator.cc
+++ b/webrtc/modules/video_coding/codecs/test/packet_manipulator.cc
@@ -46,7 +46,7 @@ int PacketManipulatorImpl::ManipulatePackets(
   packet_reader_->InitializeReading(encoded_image->_buffer,
                                     encoded_image->_length,
                                     config_.packet_size_in_bytes);
-  uint8_t* packet = NULL;
+  uint8_t* packet = nullptr;
   int nbr_bytes_to_read;
   // keep track of if we've lost any packets, since then we shall loose
   // the remains of the current frame: