base: Fix/add header #ifndef guards.

base/numerics/safe_conversions.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_H_
-#define BASE_SAFE_CONVERSIONS_H_
+#ifndef BASE_NUMERICS_SAFE_CONVERSIONS_H_
+#define BASE_NUMERICS_SAFE_CONVERSIONS_H_
 
 #include <limits>
 
 #include "base/logging.h"
 #include "base/numerics/safe_conversions_impl.h"
 
 namespace base {
 
 // Convenience function that returns true if the supplied value is in range
 // for the destination type.
@@ skipping 36 matching lines @@
       CHECK(false);
       return std::numeric_limits<Dst>::max();
   }
 
   NOTREACHED();
   return static_cast<Dst>(value);
 }
 
 }  // namespace base
 
-#endif  // BASE_SAFE_CONVERSIONS_H_
-
+#endif  // BASE_NUMERICS_SAFE_CONVERSIONS_H_