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

Will reland in two different commits to preserve git blame history.

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

Change-Id: I550da8525aeb9c5b8f96338fcf1c9714f3dcdab1
Reviewed-on: https://chromium-review.googlesource.com/554610
Reviewed-by: Henrik Kjellander <kjellander@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#18820}

webrtc/base/socketserver.h

@@ -11,9 +11,52 @@
 #ifndef WEBRTC_BASE_SOCKETSERVER_H_
 #define WEBRTC_BASE_SOCKETSERVER_H_
 
+#include <memory>
+#include "webrtc/base/socketfactory.h"
 
-// This header is deprecated and is just left here temporarily during
-// refactoring. See https://bugs.webrtc.org/7634 for more details.
-#include "webrtc/rtc_base/socketserver.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_BASE_SOCKETSERVER_H_