Add namespace and re-arrange PDFium's local copy of chromium /base.

third_party/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 PDFIUM_THIRD_PARTY_SAFE_MATH_IMPL_H_
+#define PDFIUM_THIRD_PARTY_SAFE_MATH_IMPL_H_
 
 #include <stdint.h>
 
 #include <cmath>
 #include <cstdlib>
 #include <limits>
 
 #include "../macros.h"
 #include "../template_util.h"
 #include "safe_conversions.h"
 
+namespace pdfium {
 namespace base {
 namespace internal {
 
 // Everything from here up to the floating point operations is portable C++,
 // but it may not be fast. This code could be split based on
 // platform/architecture and replaced with potentially faster implementations.
 
 // Integer promotion templates used by the portable checked integer arithmetic.
 template <size_t Size, bool IsSigned>
 struct IntegerForSizeAndSign;
@@ skipping 463 matching lines @@
                             StaticDstRangeRelationToSrcRange<T, Lhs>::value ==
                                 NUMERIC_RANGE_CONTAINED &&
                             sizeof(T) >= (2 * sizeof(Lhs)) &&
                             StaticDstRangeRelationToSrcRange<T, Rhs>::value !=
                                 NUMERIC_RANGE_CONTAINED &&
                             sizeof(T) >= (2 * sizeof(Rhs));
 };
 
 }  // namespace internal
 }  // namespace base
+}  // namespace pdfium
 
-#endif  // SAFE_MATH_IMPL_H_
+#endif  // PDFIUM_THIRD_PARTY_SAFE_MATH_IMPL_H_