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

third_party/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 PDFIUM_THIRD_PARTY_BASE_SAFE_CONVERSIONS_H_
+#define PDFIUM_THIRD_PARTY_BASE_SAFE_CONVERSIONS_H_
 
 #include <limits>
 
 #include "../logging.h"
 #include "safe_conversions_impl.h"
 
+namespace pdfium {
 namespace base {
 
 // Convenience function that returns true if the supplied value is in range
 // for the destination type.
 template <typename Dst, typename Src>
 inline bool IsValueInRangeForNumericType(Src value) {
   return internal::DstRangeRelationToSrcRange<Dst>(value) ==
          internal::RANGE_VALID;
 }
 
@@ skipping 29 matching lines @@
     case internal::RANGE_INVALID:
       CHECK(false);
       return std::numeric_limits<Dst>::max();
   }
 
   NOTREACHED();
   return static_cast<Dst>(value);
 }
 
 }  // namespace base
+}  // namespace pdfium
 
-#endif  // BASE_SAFE_CONVERSIONS_H_
+#endif  // PDFIUM_THIRD_PARTY_BASE_SAFE_CONVERSIONS_H_