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

third_party/base/numerics/safe_conversions.h

Index: third_party/base/numerics/safe_conversions.h
diff --git a/third_party/numerics/safe_conversions.h b/third_party/base/numerics/safe_conversions.h
similarity index 90%
rename from third_party/numerics/safe_conversions.h
rename to third_party/base/numerics/safe_conversions.h
index 681dc0a9cc3f46e8b759eca9a44ece5e87cff2b8..e95608e0a56a7474b21d680c29cfcfe630003b06 100644
--- a/third_party/numerics/safe_conversions.h
+++ b/third_party/base/numerics/safe_conversions.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_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
@@ -59,6 +60,7 @@ inline Dst saturated_cast(Src value) {
 }
 
 }  // namespace base
+}  // namespace pdfium
 
-#endif  // BASE_SAFE_CONVERSIONS_H_
+#endif  // PDFIUM_THIRD_PARTY_BASE_SAFE_CONVERSIONS_H_