Replace NULL with nullptr in all C++ files.

webrtc/modules/media_file/media_file_unittest.cc

Index: webrtc/modules/media_file/media_file_unittest.cc
diff --git a/webrtc/modules/media_file/media_file_unittest.cc b/webrtc/modules/media_file/media_file_unittest.cc
index 5e70a5fc387e8e2e3d163892537f688fbb234660..69e4b776406cc0464a38a4bc6b23777702d85ae6 100644
--- a/webrtc/modules/media_file/media_file_unittest.cc
+++ b/webrtc/modules/media_file/media_file_unittest.cc
@@ -18,11 +18,11 @@ class MediaFileTest : public testing::Test {
   void SetUp() {
     // Use number 0 as the the identifier and pass to CreateMediaFile.
     media_file_ = webrtc::MediaFile::CreateMediaFile(0);
-    ASSERT_TRUE(media_file_ != NULL);
+    ASSERT_TRUE(media_file_ != nullptr);
   }
   void TearDown() {
     webrtc::MediaFile::DestroyMediaFile(media_file_);
-    media_file_ = NULL;
+    media_file_ = nullptr;
   }
   webrtc::MediaFile* media_file_;
 };