Prevent base::CheckedNumeric from leaking outside of pdfium.

core/src/fxcrt/fx_safe_types.h

Index: core/src/fxcrt/fx_safe_types.h
diff --git a/core/src/fxcrt/fx_safe_types.h b/core/src/fxcrt/fx_safe_types.h
new file mode 100644
index 0000000000000000000000000000000000000000..794e1f19dc1ce3972be41b2c6a0b3605a5399810
--- /dev/null
+++ b/core/src/fxcrt/fx_safe_types.h
@@ -0,0 +1,17 @@
+// Copyright 2014 PDFium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef FX_SAFE_TYPES_H_
+#define FX_SAFE_TYPES_H_
+
+#include <stdlib.h>  // For size_t.
+
+#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;
+typedef base::CheckedNumeric<FX_FILESIZE> FX_SAFE_FILESIZE;
+
+#endif  // FX_SAFE_TYPES_H_