Forward the number of skipped frames by the OS in audio playout.

media/audio/mac/audio_auhal_mac.cc

Index: media/audio/mac/audio_auhal_mac.cc
diff --git a/media/audio/mac/audio_auhal_mac.cc b/media/audio/mac/audio_auhal_mac.cc
index 39c4610495392cac6faa92da8ffb1e55c6b05656..178cd75f67cc880a43974a969af2707d19677038 100644
--- a/media/audio/mac/audio_auhal_mac.cc
+++ b/media/audio/mac/audio_auhal_mac.cc
@@ -204,7 +204,16 @@ OSStatus AUHALStream::Render(
     AudioBufferList* data) {
   TRACE_EVENT0("audio", "AUHALStream::Render");
 
-  UpdatePlayoutTimestamp(output_time_stamp);
+  UInt32 lost_frames = UpdatePlayoutTimestampAndStats(output_time_stamp);
+
+  // Inform the source about any skipped (lost) frames. If we use a fifo this
+  // will be out of sync with the fifo pulls (different buffer sizes), so we do
+  // it here and not in ProvideInput().
+  if (lost_frames > 0) {
+    base::AutoLock auto_lock(source_lock_);
+    if (source_)
+      source_->OnSkippedData(lost_frames);
+  }
 
   // If the stream parameters change for any reason, we need to insert a FIFO
   // since the OnMoreData() pipeline can't handle frame size changes.
@@ -346,10 +355,12 @@ double AUHALStream::GetPlayoutLatency(
   return (delay_frames + hardware_latency_frames_);
 }
 
-void AUHALStream::UpdatePlayoutTimestamp(const AudioTimeStamp* timestamp) {
+UInt32 AUHALStream::UpdatePlayoutTimestampAndStats(
+    const AudioTimeStamp* timestamp) {
   if ((timestamp->mFlags & kAudioTimeStampSampleTimeValid) == 0)
     return;
 
+  UInt32 lost_frames = 0;
   if (last_sample_time_) {
     DCHECK_NE(0U, last_number_of_frames_);
     UInt32 diff =
@@ -358,7 +369,7 @@ void AUHALStream::UpdatePlayoutTimestamp(const AudioTimeStamp* timestamp) {
       DCHECK_GT(diff, last_number_of_frames_);
       // We're being asked to render samples post what we expected. Update the
       // glitch count etc and keep a record of the largest glitch.
-      auto lost_frames = diff - last_number_of_frames_;
+      lost_frames = diff - last_number_of_frames_;
       total_lost_frames_ += lost_frames;
       if (lost_frames > largest_glitch_frames_)
         largest_glitch_frames_ = lost_frames;
@@ -368,6 +379,8 @@ void AUHALStream::UpdatePlayoutTimestamp(const AudioTimeStamp* timestamp) {
 
   // Store the last sample time for use next time we get called back.
   last_sample_time_ = timestamp->mSampleTime;
+
+  return lost_frames;
 }
 
 void AUHALStream::ReportAndResetStats() {