Fix more sign comparison errors.

core/include/fpdfapi/fpdf_resource.h

Index: core/include/fpdfapi/fpdf_resource.h
diff --git a/core/include/fpdfapi/fpdf_resource.h b/core/include/fpdfapi/fpdf_resource.h
index 5b6f3498fe060f69a7ddd5066dcbca14375b4eaf..d687c97b9cde8438328cee7abc03459e854c0c6e 100644
--- a/core/include/fpdfapi/fpdf_resource.h
+++ b/core/include/fpdfapi/fpdf_resource.h
@@ -21,7 +21,6 @@ class CPDF_CMap;
 class CPDF_Color;
 class CPDF_ColorSpace;
 class CPDF_Face;
-class CPDF_Font;
 class CPDF_FontEncoding;
 class CPDF_Form;
 class CPDF_Function;
@@ -101,6 +100,7 @@ class CPDF_Font {
                                 CPDF_Dictionary* pFontDict);
   static CPDF_Font* GetStockFont(CPDF_Document* pDoc,
                                  const CFX_ByteStringC& fontname);
+  static const FX_DWORD kInvalidCharCode = static_cast<FX_DWORD>(-1);
 
   virtual ~CPDF_Font();