Replace NULL with nullptr in all C++ files.

webrtc/test/testsupport/fileutils_unittest.cc

 /*
  *  Copyright (c) 2012 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 120 matching lines @@
 #endif
   ASSERT_GT(resource.find(kTestName), 0u);
   ASSERT_GT(resource.find(kExtension), 0u);
 }
 
 TEST_F(FileUtilsTest, GetFileSizeExistingFile) {
   // Create a file with some dummy data in.
   std::string temp_filename = webrtc::test::TempFilename(
       webrtc::test::OutputPath(), "fileutils_unittest");
   FILE* file = fopen(temp_filename.c_str(), "wb");
-  ASSERT_TRUE(file != NULL) << "Failed to open file: " << temp_filename;
+  ASSERT_TRUE(file != nullptr) << "Failed to open file: " << temp_filename;
   ASSERT_GT(fprintf(file, "%s",  "Dummy data"), 0) <<
       "Failed to write to file: " << temp_filename;
   fclose(file);
   ASSERT_GT(webrtc::test::GetFileSize(std::string(temp_filename.c_str())), 0u);
   remove(temp_filename.c_str());
 }
 
 TEST_F(FileUtilsTest, GetFileSizeNonExistingFile) {
   ASSERT_EQ(0u, webrtc::test::GetFileSize("non-existing-file.tmp"));
 }
 
 }  // namespace webrtc