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

third_party/base/numerics/safe_conversions_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 BASE_SAFE_CONVERSIONS_IMPL_H_
-#define BASE_SAFE_CONVERSIONS_IMPL_H_
+#ifndef PDFIUM_THIRD_PARTY_BASE_SAFE_CONVERSIONS_IMPL_H_
+#define PDFIUM_THIRD_PARTY_BASE_SAFE_CONVERSIONS_IMPL_H_
 
 #include <limits>
 
 #include "../macros.h"
 #include "../template_util.h"
 
+namespace pdfium {
 namespace base {
 namespace internal {
 
 // The std library doesn't provide a binary max_exponent for integers, however
 // we can compute one by adding one to the number of non-sign bits. This allows
 // for accurate range comparisons between floating point and integer types.
 template <typename NumericType>
 struct MaxExponent {
   static const int value = std::numeric_limits<NumericType>::is_iec559
                                ? std::numeric_limits<NumericType>::max_exponent
@@ skipping 182 matching lines @@
 inline RangeConstraint DstRangeRelationToSrcRange(Src value) {
   COMPILE_ASSERT(std::numeric_limits<Src>::is_specialized,
                  argument_must_be_numeric);
   COMPILE_ASSERT(std::numeric_limits<Dst>::is_specialized,
                  result_must_be_numeric);
   return DstRangeRelationToSrcRangeImpl<Dst, Src>::Check(value);
 }
 
 }  // namespace internal
 }  // namespace base
+}  // namespace pdfium
 
-#endif  // BASE_SAFE_CONVERSIONS_IMPL_H_
+#endif  // PDFIUM_THIRD_PARTY_BASE_SAFE_CONVERSIONS_IMPL_H_