base: Fix/add header #ifndef guards.

base/numerics/safe_math.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_MATH_H_
-#define BASE_SAFE_MATH_H_
+#ifndef BASE_NUMERICS_SAFE_MATH_H_
+#define BASE_NUMERICS_SAFE_MATH_H_
 
 #include "base/numerics/safe_math_impl.h"
 
 namespace base {
 
 namespace internal {
 
 // CheckedNumeric implements all the logic and operators for detecting integer
 // boundary conditions such as overflow, underflow, and invalid conversions.
 // The CheckedNumeric type implicitly converts from floating point and integer
@@ skipping 245 matching lines @@
 BASE_NUMERIC_ARITHMETIC_OPERATORS(Mod, %, %= )
 
 #undef BASE_NUMERIC_ARITHMETIC_OPERATORS
 
 }  // namespace internal
 
 using internal::CheckedNumeric;
 
 }  // namespace base
 
-#endif  // BASE_SAFE_MATH_H_
+#endif  // BASE_NUMERICS_SAFE_MATH_H_