Replace NULL with nullptr or null in webrtc/base/.

webrtc/base/win32filesystem.h

Index: webrtc/base/win32filesystem.h
diff --git a/webrtc/base/win32filesystem.h b/webrtc/base/win32filesystem.h
index dd3caed385e0f5996e7291df5fbd546b568671ef..3ceaa20b06a0f98edb7f12fcb7eb0b72887f17b5 100644
--- a/webrtc/base/win32filesystem.h
+++ b/webrtc/base/win32filesystem.h
@@ -17,8 +17,8 @@ namespace rtc {
 
 class Win32Filesystem : public FilesystemInterface {
  public:
-  // Opens a file. Returns an open StreamInterface if function succeeds. Otherwise,
-  // returns NULL.
+  // Opens a file. Returns an open StreamInterface if function succeeds.
+  // Otherwise, returns null.
   virtual FileStream *OpenFile(const Pathname &filename, 
                                const std::string &mode);
 
@@ -61,7 +61,7 @@ class Win32Filesystem : public FilesystemInterface {
   // All of the following functions set pathname and return true if successful.
   // Returned paths always include a trailing backslash.
   // If create is true, the path will be recursively created.
-  // If append is non-NULL, it will be appended (and possibly created).
+  // If append is non-null, it will be appended (and possibly created).
 
   virtual std::string TempFilename(const Pathname &dir, const std::string &prefix);