Implement packet discard rate in NetEq.

BUG=webrtc:7903

Change-Id: I819c9362671ca0b02c602d53e4dc39afdd8ec465
Reviewed-on: https://chromium-review.googlesource.com/555311
Commit-Queue: Minyue Li <minyue@webrtc.org>
Reviewed-by: Henrik Lundin <henrik.lundin@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#18899}
diff --git a/webrtc/modules/audio_coding/BUILD.gn b/webrtc/modules/audio_coding/BUILD.gn
index 1aa4031..ce775dc 100644
--- a/webrtc/modules/audio_coding/BUILD.gn
+++ b/webrtc/modules/audio_coding/BUILD.gn
@@ -2114,6 +2114,7 @@
       "neteq/mock/mock_external_decoder_pcm16b.h",
       "neteq/mock/mock_packet_buffer.h",
       "neteq/mock/mock_red_payload_splitter.h",
+      "neteq/mock/mock_statistics_calculator.h",
       "neteq/nack_tracker_unittest.cc",
       "neteq/neteq_external_decoder_unittest.cc",
       "neteq/neteq_impl_unittest.cc",