Make the static variable kChunkSizeMs constexpr

This CL makes the static variable kChunkSizeMs constexpr to avoid
potential issues on some compilers.

Bug: None
Change-Id: I8e2b1819561ec96fb17d3899af95405cc36a6097
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/196640
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Per Åhgren <peah@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32795}
diff --git a/modules/audio_processing/include/audio_processing.h b/modules/audio_processing/include/audio_processing.h
index b96ce92..802ff9d 100644
--- a/modules/audio_processing/include/audio_processing.h
+++ b/modules/audio_processing/include/audio_processing.h
@@ -714,7 +714,7 @@
   static constexpr int kMaxNativeSampleRateHz =
       kNativeSampleRatesHz[kNumNativeSampleRates - 1];
 
-  static const int kChunkSizeMs = 10;
+  static constexpr int kChunkSizeMs = 10;
 };
 
 class RTC_EXPORT AudioProcessingBuilder {