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/BUILD.gn b/modules/audio_coding/BUILD.gn
index 3976600..4d3e36f 100644
--- a/modules/audio_coding/BUILD.gn
+++ b/modules/audio_coding/BUILD.gn
@@ -1029,6 +1029,7 @@
     "../../rtc_base:rtc_base_approved",
     "../../rtc_base:safe_minmax",
     "../../rtc_base:sanitizer",
+    "../../rtc_base/experiments:field_trial_parser",
     "../../rtc_base/system:fallthrough",
     "../../system_wrappers",
     "../../system_wrappers:field_trial",