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

core/include/fxcrt/fx_system.h

Index: core/include/fxcrt/fx_system.h
diff --git a/core/include/fxcrt/fx_system.h b/core/include/fxcrt/fx_system.h
index 355bd743273a1df66b530ae3bf5e51178814c56b..d6c7057af706c77440d2296ea2e6e98220ec27f7 100644
--- a/core/include/fxcrt/fx_system.h
+++ b/core/include/fxcrt/fx_system.h
@@ -276,10 +276,10 @@ int			FXSYS_round(FX_FLOAT f);
 #ifdef __cplusplus
 };
 
-#include "../../../third_party/numerics/safe_math.h"
-typedef base::CheckedNumeric<FX_DWORD> FX_SAFE_DWORD;
-typedef base::CheckedNumeric<FX_INT32> FX_SAFE_INT32;
-typedef base::CheckedNumeric<size_t>   FX_SAFE_SIZE_T;
+#include "../../../third_party/base/numerics/safe_math.h"
+typedef third_party::base::CheckedNumeric<FX_DWORD> FX_SAFE_DWORD;
+typedef third_party::base::CheckedNumeric<FX_INT32> FX_SAFE_INT32;
+typedef third_party::base::CheckedNumeric<size_t>   FX_SAFE_SIZE_T;
 
 #if defined(__clang__) || _MSC_VER >= 1700
 #define FX_FINAL final