Adding DTX controller to audio network adaptor.

webrtc/modules/audio_coding/audio_network_adaptor/dtx_controller.cc

+/*
+ *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "webrtc/modules/audio_coding/audio_network_adaptor/dtx_controller.h"
+#include "webrtc/base/checks.h"
+
+namespace webrtc {
+
+DtxController::DtxController(const Config& config)
+    : config_(config), dtx_enabled_(config_.initial_dtx_enabled) {}
+
+void DtxController::MakeDecision(
+    const NetworkMetrics& metrics,
+    AudioNetworkAdaptor::EncoderRuntimeConfig* config) {
+  // Decision on |num_channels| should not have been made.

[minyue-webrtc, 2016/09/08 14:57:54]

num_channels -> enable_dtx

+  RTC_DCHECK(!config->enable_dtx);
+
+  if (metrics.uplink_bandwidth_bps) {
+    if (dtx_enabled_ &&
+        *metrics.uplink_bandwidth_bps >= config_.dtx_disabling_bandwidth_bps) {
+      dtx_enabled_ = false;
+    } else if (!dtx_enabled_ &&
+               *metrics.uplink_bandwidth_bps <=
+                   config_.dtx_enabling_bandwidth_bps) {
+      dtx_enabled_ = true;
+    }
+  }
+  config->enable_dtx = rtc::Optional<bool>(dtx_enabled_);
+}
+
+}  // namespace webrtc