Increase the maximum supported sample rate to 384000 Hz and add tests

This CL increases the maximum supported sample rate so that all rates
up to 384000 Hz are handled.

The CL also adds tests that verifies that APM works as intended for
different combinations of number of channels and sample rates.

Bug: webrtc:10882
Change-Id: I98738e33ac21413ae00fec10bb43b8796ae2078c
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/150532
Commit-Queue: Per Åhgren <peah@webrtc.org>
Reviewed-by: Sam Zackrisson <saza@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29014}
diff --git a/modules/audio_processing/audio_buffer.h b/modules/audio_processing/audio_buffer.h
index 2d136d8..7bab26d 100644
--- a/modules/audio_processing/audio_buffer.h
+++ b/modules/audio_processing/audio_buffer.h
@@ -33,6 +33,7 @@
 class AudioBuffer {
  public:
   static const int kSplitBandSize = 160;
+  static const size_t kMaxSampleRate = 384000;
   AudioBuffer(size_t input_rate,
               size_t input_num_channels,
               size_t buffer_rate,