base: Fix/add header #ifndef guards.

base/numerics/safe_conversions_impl.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef BASE_SAFE_CONVERSIONS_IMPL_H_
-#define BASE_SAFE_CONVERSIONS_IMPL_H_
+#ifndef BASE_NUMERICS_SAFE_CONVERSIONS_IMPL_H_
+#define BASE_NUMERICS_SAFE_CONVERSIONS_IMPL_H_
 
 #include <limits>
 
 #include "base/template_util.h"
 
 namespace base {
 namespace internal {
 
 // The std library doesn't provide a binary max_exponent for integers, however
 // we can compute one by adding one to the number of non-sign bits. This allows
@@ skipping 188 matching lines @@
   static_assert(std::numeric_limits<Src>::is_specialized,
                 "Argument must be numeric.");
   static_assert(std::numeric_limits<Dst>::is_specialized,
                 "Result must be numeric.");
   return DstRangeRelationToSrcRangeImpl<Dst, Src>::Check(value);
 }
 
 }  // namespace internal
 }  // namespace base
 
-#endif  // BASE_SAFE_CONVERSIONS_IMPL_H_
-
+#endif  // BASE_NUMERICS_SAFE_CONVERSIONS_IMPL_H_