Add ability for audioproc_f to operate on any AudioProcessing object.

This CL extends the WebRTC testing API to allow audioproc_f -based
testing using a pre-created AudioProcessing object. This is an
important feature to allow testing any AudioProcessing objects
that are injected into WebRTC.

Beyond adding this, the CL also changes the simulation code to
operate on a scoped_refptr<AudioProcessing> object instead of a
std::unique<AudioProcessing> object

Bug: webrtc:5298
Change-Id: I70179f19518fc583ad0101bd59c038478a3cc23d
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/175568
Commit-Queue: Per Åhgren <peah@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Sam Zackrisson <saza@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31319}

modules/audio_processing/test/wav_based_simulator.h

@@ -23,6 +23,7 @@ namespace test {
 class WavBasedSimulator final : public AudioProcessingSimulator {
  public:
   WavBasedSimulator(const SimulationSettings& settings,
+                    rtc::scoped_refptr<AudioProcessing> audio_processing,
                     std::unique_ptr<AudioProcessingBuilder> ap_builder);
   ~WavBasedSimulator() override;