Pull out the PostFilter to its own NonlinearBeamformer API

webrtc/common_audio/lapped_transform.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 65 matching lines @@
       cplx_length_(RealFourier::ComplexLength(fft_->order())),
       real_buf_(num_in_channels,
                 block_length_,
                 RealFourier::kFftBufferAlignment),
       cplx_pre_(num_in_channels,
                 cplx_length_,
                 RealFourier::kFftBufferAlignment),
       cplx_post_(num_out_channels,
                  cplx_length_,
                  RealFourier::kFftBufferAlignment) {
-  RTC_CHECK(num_in_channels_ > 0 && num_out_channels_ > 0);
+  RTC_CHECK(num_in_channels_ > 0);
   RTC_CHECK_GT(block_length_, 0u);
   RTC_CHECK_GT(chunk_length_, 0u);
   RTC_CHECK(block_processor_);
 
   // block_length_ power of 2?
   RTC_CHECK_EQ(0u, block_length_ & (block_length_ - 1));
 }
 
 void LappedTransform::ProcessChunk(const float* const* in_chunk,
                                    float* const* out_chunk) {
   blocker_.ProcessChunk(in_chunk, chunk_length_, num_in_channels_,
                         num_out_channels_, out_chunk);
 }
 
 }  // namespace webrtc