Improve buffer level estimation with DTX and add CNG time stretching.

The functionality is hidden behind field trial for experimentation.

Bug: webrtc:10736
Change-Id: I1daf60966717c3ea43bf6ee16d190290ab740ce7
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/144059
Commit-Queue: Jakob Ivarsson <jakobi@webrtc.org>
Reviewed-by: Minyue Li <minyue@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#28474}
diff --git a/modules/audio_coding/neteq/packet_buffer.h b/modules/audio_coding/neteq/packet_buffer.h
index 0837027..c00db29 100644
--- a/modules/audio_coding/neteq/packet_buffer.h
+++ b/modules/audio_coding/neteq/packet_buffer.h
@@ -123,7 +123,9 @@
 
   // Returns the total duration in samples that the packets in the buffer spans
   // across.
-  virtual size_t GetSpanSamples(size_t last_decoded_length) const;
+  virtual size_t GetSpanSamples(size_t last_decoded_length,
+                                size_t sample_rate,
+                                bool count_dtx_waiting_time) const;
 
   // Returns true if the packet buffer contains any DTX or CNG packets.
   virtual bool ContainsDtxOrCngPacket(