Express audio delay more precisely in frames rather than milliseconds.

media/audio/audio_parameters.h

Index: media/audio/audio_parameters.h
diff --git a/media/audio/audio_parameters.h b/media/audio/audio_parameters.h
index 3e6603bd075368cb3725e2f847d5ff86c6c7bcf8..2735d79af927889eef786b9acd907140230fd3ac 100644
--- a/media/audio/audio_parameters.h
+++ b/media/audio/audio_parameters.h
@@ -125,6 +125,12 @@ class MEDIA_EXPORT AudioParameters {
   // Returns the number of bytes representing a frame of audio.
   int GetBytesPerFrame() const;
 
+  // Returns the number of microseconds per frame of audio. Intentionally
+  // reported as a double to surface of partial microseconds per frame, which
+  // is common for many sample rates. Failing to account for these nanoseconds
+  // can lead to audio/video sync drift.
+  double GetMicrosecondsPerFrame() const;
+
   // Returns the duration of this buffer as calculated from frames_per_buffer()
   // and sample_rate().
   base::TimeDelta GetBufferDuration() const;