Revert of Remove remains of webrtc/base (patchset #7 id:120001 of https://codereview.webrtc.org/297…

webrtc/base/safe_compare.h

+/*
+ *  Copyright 2016 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.
+ */
+
+// This file defines six constexpr functions:
+//
+//   rtc::SafeEq  // ==
+//   rtc::SafeNe  // !=
+//   rtc::SafeLt  // <
+//   rtc::SafeLe  // <=
+//   rtc::SafeGt  // >
+//   rtc::SafeGe  // >=
+//
+// They each accept two arguments of arbitrary types, and in almost all cases,
+// they simply call the appropriate comparison operator. However, if both
+// arguments are integers, they don't compare them using C++'s quirky rules,
+// but instead adhere to the true mathematical definitions. It is as if the
+// arguments were first converted to infinite-range signed integers, and then
+// compared, although of course nothing expensive like that actually takes
+// place. In practice, for signed/signed and unsigned/unsigned comparisons and
+// some mixed-signed comparisons with a compile-time constant, the overhead is
+// zero; in the remaining cases, it is just a few machine instructions (no
+// branches).
+
+#ifndef WEBRTC_BASE_SAFE_COMPARE_H_
+#define WEBRTC_BASE_SAFE_COMPARE_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/safe_compare.h"
+
+#endif  // WEBRTC_BASE_SAFE_COMPARE_H_