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

webrtc/base/bitbuffer.cc

 /*
  *  Copyright 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 184 matching lines @@
   if ((unsigned_val & 1) == 0) {
     *val = -static_cast<int32_t>(unsigned_val / 2);
   } else {
     *val = (unsigned_val + 1) / 2;
   }
   return true;
 }
 
 void BitBuffer::GetCurrentOffset(
     size_t* out_byte_offset, size_t* out_bit_offset) {
-  RTC_CHECK(out_byte_offset != NULL);
-  RTC_CHECK(out_bit_offset != NULL);
+  RTC_CHECK(out_byte_offset != nullptr);
+  RTC_CHECK(out_bit_offset != nullptr);
   *out_byte_offset = byte_offset_;
   *out_bit_offset = bit_offset_;
 }
 
 bool BitBuffer::Seek(size_t byte_offset, size_t bit_offset) {
   if (byte_offset > byte_count_ || bit_offset > 7 ||
       (byte_offset == byte_count_ && bit_offset > 0)) {
     return false;
   }
   byte_offset_ = byte_offset;
@@ skipping 84 matching lines @@
     return WriteExponentialGolomb((signed_val * 2) - 1);
   } else {
     if (val == std::numeric_limits<int32_t>::min())
       return false;  // Not supported, would cause overflow.
     uint32_t signed_val = -val;
     return WriteExponentialGolomb(signed_val * 2);
   }
 }
 
 }  // namespace rtc