Split P2PTransportChannel

This patch moves the logic for
- selection of connection to ping
- selection of connection to use
- selection of connection to prune

into own file and puts it behind a new interface called 'IceControllerInterface'.

BUG=webrtc:10647

Change-Id: I10228b3edd361d3200fa4a734d74a319560966c9
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/158205
Reviewed-by: Qingsi Wang <qingsi@webrtc.org>
Reviewed-by: Honghai Zhang <honghaiz@webrtc.org>
Commit-Queue: Jonas Oreland <jonaso@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29850}

p2p/base/ice_controller_interface.cc

@@ -0,0 +1,55 @@
+/*
+ *  Copyright 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.
+ */
+
+#include "p2p/base/ice_controller_interface.h"
+
+#include <string>
+
+namespace cricket {
+
+std::string IceControllerEvent::ToString() const {
+  std::string reason;
+  switch (type) {
+    case REMOTE_CANDIDATE_GENERATION_CHANGE:
+      reason = "remote candidate generation maybe changed";
+      break;
+    case NETWORK_PREFERENCE_CHANGE:
+      reason = "network preference changed";
+      break;
+    case NEW_CONNECTION_FROM_LOCAL_CANDIDATE:
+      reason = "new candidate pairs created from a new local candidate";
+      break;
+    case NEW_CONNECTION_FROM_REMOTE_CANDIDATE:
+      reason = "new candidate pairs created from a new remote candidate";
+      break;
+    case NEW_CONNECTION_FROM_UNKNOWN_REMOTE_ADDRESS:
+      reason = "a new candidate pair created from an unknown remote address";
+      break;
+    case NOMINATION_ON_CONTROLLED_SIDE:
+      reason = "nomination on the controlled side";
+      break;
+    case DATA_RECEIVED:
+      reason = "data received";
+      break;
+    case CONNECT_STATE_CHANGE:
+      reason = "candidate pair state changed";
+      break;
+    case SELECTED_CONNECTION_DESTROYED:
+      reason = "selected candidate pair destroyed";
+      break;
+  }
+  if (dampening_delay) {
+    reason += " (after switching dampening interval: " +
+              std::to_string(dampening_delay) + ")";
+  }
+  return reason;
+}
+
+}  // namespace cricket