Merge to XFA: Add test for CPDF_SyntaxParser::ReadHexString.

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index b5b660a43fbb4efedca6c8b7f60e1f44aa8b8cff..f2fda1c6357d5a9033849f1e7a066c8bb1e32935 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -1477,6 +1477,7 @@ test("pdfium_unittests") {
     "core/src/fpdfapi/fpdf_font/fpdf_font_unittest.cpp",
     "core/src/fpdfapi/fpdf_page/fpdf_page_parser_old_unittest.cpp",
     "core/src/fpdfapi/fpdf_parser/fpdf_parser_decode_unittest.cpp",
+    "core/src/fpdfapi/fpdf_parser/fpdf_parser_parser_unittest.cpp",
     "core/src/fxcodec/codec/fx_codec_jpx_unittest.cpp",
     "core/src/fxcrt/fx_basic_bstring_unittest.cpp",
     "core/src/fxcrt/fx_basic_memmgr_unittest.cpp",