Adding initial support for lock-less informing of muting

This CL adds the initial support for letting APM know when its output
will be used or not.
It also adds a new method for passing RuntimeInformation to APM that
returns a bool indicating the success of the passing of information.

Bug: b/177830919
Change-Id: Ic2e1b92c37241d74ca6394b785b91736ca7532aa
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/206061
Commit-Queue: Per Åhgren <peah@webrtc.org>
Reviewed-by: Alessio Bazzica <alessiob@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33201}

modules/audio_processing/include/audio_processing.h

@@ -525,12 +525,18 @@ class RTC_EXPORT AudioProcessing : public rtc::RefCountInterface {
   // Set to true when the output of AudioProcessing will be muted or in some
   // other way not used. Ideally, the captured audio would still be processed,
   // but some components may change behavior based on this information.
-  // Default false.
+  // Default false. This method takes a lock. To achieve this in a lock-less
+  // manner the PostRuntimeSetting can instead be used.
   virtual void set_output_will_be_muted(bool muted) = 0;
 
-  // Enqueue a runtime setting.
+  // Enqueues a runtime setting.
   virtual void SetRuntimeSetting(RuntimeSetting setting) = 0;
 
+  // Enqueues a runtime setting. Returns a bool indicating whether the
+  // enqueueing was successfull.
+  // TODO(b/177830919): Change this to pure virtual.
+  virtual bool PostRuntimeSetting(RuntimeSetting setting) { return false; }
+
   // Accepts and produces a 10 ms frame interleaved 16 bit integer audio as
   // specified in |input_config| and |output_config|. |src| and |dest| may use
   // the same memory, if desired.