Replace NULL with nullptr in webrtc/video.

webrtc/video/video_decoder.cc

 /*
  *  Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 56 matching lines @@
   RTC_CHECK(decoder_type_ != kUnsupportedCodec)
       << "Decoder requesting fallback to codec not supported in software.";
   LOG(LS_WARNING) << "Decoder falling back to software decoding.";
   fallback_decoder_.reset(VideoDecoder::Create(decoder_type_));
   if (fallback_decoder_->InitDecode(&codec_settings_, number_of_cores_) !=
       WEBRTC_VIDEO_CODEC_OK) {
     LOG(LS_ERROR) << "Failed to initialize software-decoder fallback.";
     fallback_decoder_.reset();
     return false;
   }
-  if (callback_ != nullptr)
+  if (callback_)
     fallback_decoder_->RegisterDecodeCompleteCallback(callback_);
   fallback_implementation_name_ =
       std::string(fallback_decoder_->ImplementationName()) +
       " (fallback from: " + decoder_->ImplementationName() + ")";
   return true;
 }
 
 int32_t VideoDecoderSoftwareFallbackWrapper::Decode(
     const EncodedImage& input_image,
     bool missing_frames,
@@ skipping 78 matching lines @@
 
 int32_t NullVideoDecoder::Release() {
   return WEBRTC_VIDEO_CODEC_OK;
 }
 
 const char* NullVideoDecoder::ImplementationName() const {
   return "NullVideoDecoder";
 }
 
 }  // namespace webrtc