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

third_party/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 PDFIUM_THIRD_PARTY_BASE_SAFE_MATH_H_
+#define PDFIUM_THIRD_PARTY_BASE_SAFE_MATH_H_
 
 #include "safe_math_impl.h"
 
+namespace pdfium {
 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
 // data types, and contains overloads for basic arithmetic operations (i.e.: +,
 // -, *, /, %).
 //
 // The following methods convert from CheckedNumeric to standard numeric values:
 // IsValid() - Returns true if the underlying numeric value is valid (i.e. has
@@ skipping 238 matching lines @@
 BASE_NUMERIC_ARITHMETIC_OPERATORS(Div, /, /= )
 BASE_NUMERIC_ARITHMETIC_OPERATORS(Mod, %, %= )
 
 #undef BASE_NUMERIC_ARITHMETIC_OPERATORS
 
 }  // namespace internal
 
 using internal::CheckedNumeric;
 
 }  // namespace base
+}  // namespace pdfium
 
-#endif  // BASE_SAFE_MATH_H_
+#endif  // PDFIUM_THIRD_PARTY_BASE_SAFE_MATH_H_