Adding full initial version of delay estimation functionality in echo canceller 3

webrtc/modules/audio_processing/aec3/echo_canceller3.cc

Index: webrtc/modules/audio_processing/aec3/echo_canceller3.cc
diff --git a/webrtc/modules/audio_processing/aec3/echo_canceller3.cc b/webrtc/modules/audio_processing/aec3/echo_canceller3.cc
index ec7b55a215b3d7d50ceec1a4c260ceb4feda476d..a4b796d969d2132c3a0ee72b43d25d8662e30471 100644
--- a/webrtc/modules/audio_processing/aec3/echo_canceller3.cc
+++ b/webrtc/modules/audio_processing/aec3/echo_canceller3.cc
@@ -227,6 +227,8 @@ EchoCanceller3::EchoCanceller3(int sample_rate_hz,
                                  std::vector<float>(frame_length_, 0.f)),
       block_(num_bands_, std::vector<float>(kBlockSize, 0.f)),
       sub_frame_view_(num_bands_) {
+  RTC_DCHECK(ValidFullBandRate(sample_rate_hz_));
+
   std::unique_ptr<CascadedBiQuadFilter> render_highpass_filter;
   if (use_highpass_filter) {
     render_highpass_filter.reset(new CascadedBiQuadFilter(