Drop WebRTC audio data if OS has skipped frames.

media/base/audio_pull_fifo.h

Index: media/base/audio_pull_fifo.h
diff --git a/media/base/audio_pull_fifo.h b/media/base/audio_pull_fifo.h
index a839c8d6c8ed59d8e97b8e27ca00844e7d02d4ec..79173f55641170c31572de45122d205f18fb2e59 100644
--- a/media/base/audio_pull_fifo.h
+++ b/media/base/audio_pull_fifo.h
@@ -41,6 +41,9 @@ class MEDIA_EXPORT AudioPullFifo {
   // Empties the FIFO without deallocating any memory.
   void Clear();
 
+  // Returns the size of the fifo in number of frames.
+  int SizeInFrames() const;
+
  private:
   // Attempt to fulfill the request using what is available in the FIFO.
   // Append new data to the |destination| starting at |write_pos|.