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/base/socketaddresspair.h

@@ -1,41 +0,0 @@
-/*
- *  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_BASE_SOCKETADDRESSPAIR_H__
-#define WEBRTC_BASE_SOCKETADDRESSPAIR_H__
-
-#include "webrtc/base/socketaddress.h"
-
-namespace rtc {
-
-// Records a pair (source,destination) of socket addresses.  The two addresses
-// identify a connection between two machines.  (For UDP, this "connection" is
-// not maintained explicitly in a socket.)
-class SocketAddressPair {
-public:
-  SocketAddressPair() {}
-  SocketAddressPair(const SocketAddress& srs, const SocketAddress& dest);
-
-  const SocketAddress& source() const { return src_; }
-  const SocketAddress& destination() const { return dest_; }
-
-  bool operator ==(const SocketAddressPair& r) const;
-  bool operator <(const SocketAddressPair& r) const;
-
-  size_t Hash() const;
-
-private:
-  SocketAddress src_;
-  SocketAddress dest_;
-};
-
-} // namespace rtc
-
-#endif // WEBRTC_BASE_SOCKETADDRESSPAIR_H__