Replace NULL with nullptr in webrtc/video.

webrtc/video/replay.cc

Index: webrtc/video/replay.cc
diff --git a/webrtc/video/replay.cc b/webrtc/video/replay.cc
index affd033ff9d88fa22524ce7847eeb6e9dbf0412d..1830d515020b60ee95ff73cc9fab1c9cb096c92f 100644
--- a/webrtc/video/replay.cc
+++ b/webrtc/video/replay.cc
@@ -148,19 +148,19 @@ class FileRenderPassthrough : public rtc::VideoSinkInterface<VideoFrame> {
         last_height_(0) {}
 
   ~FileRenderPassthrough() {
-    if (file_ != nullptr)
+    if (file_)
       fclose(file_);
   }
 
  private:
   void OnFrame(const VideoFrame& video_frame) override {
-    if (renderer_ != nullptr)
+    if (renderer_)
       renderer_->OnFrame(video_frame);
     if (basename_.empty())
       return;
     if (last_width_ != video_frame.width() ||
         last_height_ != video_frame.height()) {
-      if (file_ != nullptr)
+      if (file_)
         fclose(file_);
       std::stringstream filename;
       filename << basename_;
@@ -194,7 +194,7 @@ class DecoderBitstreamFileWriter : public EncodedFrameObserver {
  public:
   explicit DecoderBitstreamFileWriter(const char* filename)
       : file_(fopen(filename, "wb")) {
-    RTC_DCHECK(file_ != nullptr);
+    RTC_DCHECK(file_);
   }
   ~DecoderBitstreamFileWriter() { fclose(file_); }