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 97%
rename from third_party/numerics/safe_conversions.h
rename to third_party/base/numerics/safe_conversions.h
index 681dc0a9cc3f46e8b759eca9a44ece5e87cff2b8..b783d23e393b866d5417485c3f5012f2c70f5085 100644
--- a/third_party/numerics/safe_conversions.h
+++ b/third_party/base/numerics/safe_conversions.h
@@ -10,6 +10,7 @@
 #include "../logging.h"
 #include "safe_conversions_impl.h"
 
+namespace third_party {
 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 third_party
 
 #endif  // BASE_SAFE_CONVERSIONS_H_