Add base class NetworkPredictor and NetworkPredictorFactory and wire up.

Add base class NetworkPredictor and NetworkPredictorFactory in /api, make it possible to inject customized NetworkPredictor in PeerConnectionFactory level. The NetworkPredictor object will be pass down to GoogCCNetworkControl and DelayBasedBwe.

Bug: webrtc:10492
Change-Id: Iceeadbe1c9388b11ce4ac01ee56554cb0bf64d04
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/130201
Commit-Queue: Ying Wang <yinwa@webrtc.org>
Reviewed-by: Per Kjellander <perkj@webrtc.org>
Reviewed-by: Stefan Holmer <stefan@webrtc.org>
Reviewed-by: Sami Kalliomäki <sakal@webrtc.org>
Reviewed-by: Christoffer Rodbro <crodbro@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27543}

api/network_state_predictor.h

@@ -0,0 +1,56 @@
+/*
+ *  Copyright (c) 2019 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.
+ */
+
+#ifndef API_NETWORK_STATE_PREDICTOR_H_
+#define API_NETWORK_STATE_PREDICTOR_H_
+
+#include <memory>
+#include <vector>
+
+namespace webrtc {
+
+enum class BandwidthUsage {
+  kBwNormal = 0,
+  kBwUnderusing = 1,
+  kBwOverusing = 2,
+  kLast
+};
+
+// TODO(yinwa): work in progress. API in class NetworkStatePredictor should not
+// be used by other users until this comment is removed.
+
+// NetworkStatePredictor predict network state based on current network metrics.
+// Usage:
+// Setup by calling Initialize.
+// For each update, call Update. Update returns network state
+// prediction.
+class NetworkStatePredictor {
+ public:
+  virtual ~NetworkStatePredictor() {}
+
+  // Returns current network state prediction.
+  // Inputs:  send_time_ms - packet send time.
+  //          arrival_time_ms - packet arrival time.
+  //          network_state - computed network state.
+  virtual BandwidthUsage Update(int64_t send_time_ms,
+                                int64_t arrival_time_ms,
+                                BandwidthUsage network_state) = 0;
+};
+
+class NetworkStatePredictorFactoryInterface {
+ public:
+  virtual std::unique_ptr<NetworkStatePredictor>
+  CreateNetworkStatePredictor() = 0;
+  virtual ~NetworkStatePredictorFactoryInterface() = default;
+};
+
+}  // namespace webrtc
+
+#endif  // API_NETWORK_STATE_PREDICTOR_H_