Resolve fde_xml.h header collision

R=thestig@chromium.org

Review URL: https://codereview.chromium.org/1581823002 .
diff --git a/xfa.gyp b/xfa.gyp
index 810464e..8e1ddec 100644
--- a/xfa.gyp
+++ b/xfa.gyp
@@ -134,8 +134,8 @@
         "xfa/src/fdp/src/fde/fde_render.h",
         "xfa/src/fdp/src/tto/fde_textout.cpp",
         "xfa/src/fdp/src/tto/fde_textout.h",
-        "xfa/src/fdp/src/xml/fde_xml.cpp",
-        "xfa/src/fdp/src/xml/fde_xml.h",
+        "xfa/src/fdp/src/xml/fde_xml_imp.cpp",
+        "xfa/src/fdp/src/xml/fde_xml_imp.h",
         "xfa/src/fee/include/fx_wordbreak.h",
         "xfa/src/fee/include/ifde_txtedtbuf.h",
         "xfa/src/fee/include/ifde_txtedtengine.h",