Replace NULL with nullptr or null in webrtc/audio/ and common_audio/.

webrtc/common_audio/fir_filter.cc

 /*
  *  Copyright (c) 2014 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 22 matching lines @@
   size_t state_length_;
   std::unique_ptr<float[]> coefficients_;
   std::unique_ptr<float[]> state_;
 };
 
 FIRFilter* FIRFilter::Create(const float* coefficients,
                              size_t coefficients_length,
                              size_t max_input_length) {
   if (!coefficients || coefficients_length <= 0 || max_input_length <= 0) {
     RTC_NOTREACHED();
-    return NULL;
+    return nullptr;
   }
 
-  FIRFilter* filter = NULL;
+  FIRFilter* filter = nullptr;
 // If we know the minimum architecture at compile time, avoid CPU detection.
 #if defined(WEBRTC_ARCH_X86_FAMILY)
 #if defined(__SSE2__)
   filter =
       new FIRFilterSSE2(coefficients, coefficients_length, max_input_length);
 #else
   // x86 CPU detection required.
   if (WebRtc_GetCPUInfo(kSSE2)) {
     filter =
         new FIRFilterSSE2(coefficients, coefficients_length, max_input_length);
@@ skipping 44 matching lines @@
         state_.get(), &in[length - state_length_], state_length_ * sizeof(*in));
   } else {
     memmove(state_.get(),
             &state_[length],
             (state_length_ - length) * sizeof(state_[0]));
     memcpy(&state_[state_length_ - length], in, length * sizeof(*in));
   }
 }
 
 }  // namespace webrtc