Bug 1656438 - Only raise the FramesProcessedEvent once there is no silence. r=padenot

Because an audio driver starts out with its fallback driver running the graph,
we might use unnecessary amounts of silence for the verification. Especially
with the `GoFaster()` mode turned on, as the fallback driver's thread runs
rarely compared to how often we are feeding the graph audio data from the
MockCubebStream.

Differential Revision: https://phabricator.services.mozilla.com/D89753

dom/media/gtest/AudioVerifier.h

@@ -56,6 +56,9 @@ class AudioVerifier {
                                sin(2 * M_PI * mFrequency / mRate));
   }
 
+  bool PreSilenceEnded() const {
+    return mTotalFramesSoFar > mPreSilenceSamples;
+  }
   uint64_t PreSilenceSamples() const { return mPreSilenceSamples; }
   uint32_t CountDiscontinuities() const { return mDiscontinuitiesCount; }
 

dom/media/gtest/MockCubeb.h

@@ -225,7 +225,9 @@ class MockCubebStream {
       mAudioVerifier.AppendDataInterleaved(mOutputBuffer, outframes,
                                            NUM_OF_CHANNELS);
 
+      if (mAudioVerifier.PreSilenceEnded()) {
         mFramesProcessedEvent.Notify(outframes);
+      }
 
       if (outframes < NUM_OF_FRAMES) {
         mStateCallback(stream, mUserPtr, CUBEB_STATE_DRAINED);