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

third_party/base/numerics/safe_math.h

Index: third_party/base/numerics/safe_math.h
diff --git a/third_party/numerics/safe_math.h b/third_party/base/numerics/safe_math.h
similarity index 99%
rename from third_party/numerics/safe_math.h
rename to third_party/base/numerics/safe_math.h
index 4b38ff2b1f018cb300377cfe12679e12330f0d84..06fbe0ddc3a5b4f11431c08124d500950aeb20d8 100644
--- a/third_party/numerics/safe_math.h
+++ b/third_party/base/numerics/safe_math.h
@@ -7,8 +7,8 @@
 
 #include "safe_math_impl.h"
 
+namespace third_party {
 namespace base {
-
 namespace internal {
 
 // CheckedNumeric implements all the logic and operators for detecting integer
@@ -267,5 +267,6 @@ BASE_NUMERIC_ARITHMETIC_OPERATORS(Mod, %, %= )
 using internal::CheckedNumeric;
 
 }  // namespace base
+}  // namespace third_party
 
 #endif  // BASE_SAFE_MATH_H_