Simplification and refactoring of the AudioBuffer code

This CL performs a major refactoring and simplification
of the AudioBuffer code that.
-Removes 7 of the 9 internal buffers of the AudioBuffer.
-Avoids the implicit copying required to keep the
 internal buffers in sync.
-Removes all code relating to handling of fixed-point
 sample data in the AudioBuffer.
-Changes the naming of the class methods to reflect
 that only floating point is handled.
-Corrects some bugs in the code.
-Extends the handling of internal downmixing to be
 more generic.

Bug: webrtc:10882
Change-Id: I12c8af156fbe366b154744a0a1b3d926bf7be572
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/149828
Commit-Queue: Per Åhgren <peah@webrtc.org>
Reviewed-by: Gustaf Ullberg <gustaf@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#28928}
diff --git a/modules/audio_processing/voice_detection_impl.cc b/modules/audio_processing/voice_detection_impl.cc
index 3b0eb7c..80b633c 100644
--- a/modules/audio_processing/voice_detection_impl.cc
+++ b/modules/audio_processing/voice_detection_impl.cc
@@ -63,17 +63,16 @@
   std::array<int16_t, AudioBuffer::kMaxSplitFrameLength> mixed_low_pass_data;
   rtc::ArrayView<const int16_t> mixed_low_pass(mixed_low_pass_data.data(),
                                                audio->num_frames_per_band());
-  if (audio->num_proc_channels() == 1) {
-    FloatS16ToS16(audio->split_bands_const_f(0)[kBand0To8kHz],
+  if (audio->num_channels() == 1) {
+    FloatS16ToS16(audio->split_bands_const(0)[kBand0To8kHz],
                   audio->num_frames_per_band(), mixed_low_pass_data.data());
   } else {
     const int num_channels = static_cast<int>(audio->num_channels());
     for (size_t i = 0; i < audio->num_frames_per_band(); ++i) {
       int32_t value =
-          FloatS16ToS16(audio->split_channels_const_f(kBand0To8kHz)[0][i]);
+          FloatS16ToS16(audio->split_channels_const(kBand0To8kHz)[0][i]);
       for (int j = 1; j < num_channels; ++j) {
-        value +=
-            FloatS16ToS16(audio->split_channels_const_f(kBand0To8kHz)[j][i]);
+        value += FloatS16ToS16(audio->split_channels_const(kBand0To8kHz)[j][i]);
       }
       mixed_low_pass_data[i] = value / num_channels;
     }