Reland "Move webrtc/{base => rtc_base}" (https://codereview.webrtc.org/2877023002)

Reland the base->rtc_base without adding stub headers (will be
done in follow-up CL). This preserves git blame history of all files.

BUG=webrtc:7634
NOTRY=True
TBR=kwiberg@webrtc.org

Change-Id: Iea3bb6f3f67b8374c96337b63e8f5aa3e6181012
Reviewed-on: https://chromium-review.googlesource.com/554611
Reviewed-by: Henrik Kjellander <kjellander@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#18821}

webrtc/rtc_base/socketserver.h

@@ -0,0 +1,62 @@
+/*
+ *  Copyright 2004 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 WEBRTC_RTC_BASE_SOCKETSERVER_H_
+#define WEBRTC_RTC_BASE_SOCKETSERVER_H_
+
+#include <memory>
+#include "webrtc/base/socketfactory.h"
+
+namespace rtc {
+
+class MessageQueue;
+// Needs to be forward declared because there's a circular dependency between
+// NetworkMonitor and Thread.
+// TODO(deadbeef): Fix this.
+class NetworkBinderInterface;
+
+// Provides the ability to wait for activity on a set of sockets.  The Thread
+// class provides a nice wrapper on a socket server.
+//
+// The server is also a socket factory.  The sockets it creates will be
+// notified of asynchronous I/O from this server's Wait method.
+class SocketServer : public SocketFactory {
+ public:
+  static const int kForever = -1;
+
+  static std::unique_ptr<SocketServer> CreateDefault();
+  // When the socket server is installed into a Thread, this function is
+  // called to allow the socket server to use the thread's message queue for
+  // any messaging that it might need to perform.
+  virtual void SetMessageQueue(MessageQueue* queue) {}
+
+  // Sleeps until:
+  //  1) cms milliseconds have elapsed (unless cms == kForever)
+  //  2) WakeUp() is called
+  // While sleeping, I/O is performed if process_io is true.
+  virtual bool Wait(int cms, bool process_io) = 0;
+
+  // Causes the current wait (if one is in progress) to wake up.
+  virtual void WakeUp() = 0;
+
+  // A network binder will bind the created sockets to a network.
+  // It is only used in PhysicalSocketServer.
+  void set_network_binder(NetworkBinderInterface* binder) {
+    network_binder_ = binder;
+  }
+  NetworkBinderInterface* network_binder() const { return network_binder_; }
+
+ private:
+  NetworkBinderInterface* network_binder_ = nullptr;
+};
+
+}  // namespace rtc
+
+#endif  // WEBRTC_RTC_BASE_SOCKETSERVER_H_