base: Fix/add header #ifndef guards.

base/numerics/safe_math_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 SAFE_MATH_IMPL_H_
-#define SAFE_MATH_IMPL_H_
+#ifndef BASE_NUMERICS_SAFE_MATH_IMPL_H_
+#define BASE_NUMERICS_SAFE_MATH_IMPL_H_
 
 #include <stdint.h>
 
 #include <cmath>
 #include <cstdlib>
 #include <limits>
 
 #include "base/numerics/safe_conversions.h"
 #include "base/template_util.h"
 
@@ skipping 474 matching lines @@
                                 NUMERIC_RANGE_CONTAINED &&
                             sizeof(T) >= (2 * sizeof(Lhs)) &&
                             StaticDstRangeRelationToSrcRange<T, Rhs>::value !=
                                 NUMERIC_RANGE_CONTAINED &&
                             sizeof(T) >= (2 * sizeof(Rhs));
 };
 
 }  // namespace internal
 }  // namespace base
 
-#endif  // SAFE_MATH_IMPL_H_
+#endif  // BASE_NUMERICS_SAFE_MATH_IMPL_H_