Use backticks not vertical bars to denote variables in comments for /modules/audio_processing

Bug: webrtc:12338
Change-Id: I85bff694dd2ead83c939c4d1945eff82e1296001
No-Presubmit: True
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/227161
Commit-Queue: Artem Titov <titovartem@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34690}
diff --git a/modules/audio_processing/test/test_utils.h b/modules/audio_processing/test/test_utils.h
index e2d243e..30674cb 100644
--- a/modules/audio_processing/test/test_utils.h
+++ b/modules/audio_processing/test/test_utils.h
@@ -78,7 +78,7 @@
   explicit ChannelBufferWavReader(std::unique_ptr<WavReader> file);
   ~ChannelBufferWavReader();
 
-  // Reads data from the file according to the |buffer| format. Returns false if
+  // Reads data from the file according to the `buffer` format. Returns false if
   // a full buffer can't be read from the file.
   bool Read(ChannelBuffer<float>* buffer);
 
@@ -115,7 +115,7 @@
       delete;
   ~ChannelBufferVectorWriter();
 
-  // Creates an interleaved copy of |buffer|, converts the samples to float S16
+  // Creates an interleaved copy of `buffer`, converts the samples to float S16
   // and appends the result to output_.
   void Write(const ChannelBuffer<float>& buffer);