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

third_party/base/numerics/safe_conversions_impl.h

Index: third_party/base/numerics/safe_conversions_impl.h
diff --git a/third_party/numerics/safe_conversions_impl.h b/third_party/base/numerics/safe_conversions_impl.h
similarity index 97%
rename from third_party/numerics/safe_conversions_impl.h
rename to third_party/base/numerics/safe_conversions_impl.h
index a357e518d1f5fcd0211177fa7cdacce5862eecb6..7c88dda0a85c98fcc54d58e3d4227bff04ab05cf 100644
--- a/third_party/numerics/safe_conversions_impl.h
+++ b/third_party/base/numerics/safe_conversions_impl.h
@@ -2,14 +2,15 @@
 // 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 {
 
@@ -212,6 +213,7 @@ inline RangeConstraint DstRangeRelationToSrcRange(Src value) {
 
 }  // namespace internal
 }  // namespace base
+}  // namespace pdfium
 
-#endif  // BASE_SAFE_CONVERSIONS_IMPL_H_
+#endif  // PDFIUM_THIRD_PARTY_BASE_SAFE_CONVERSIONS_IMPL_H_