Revert "Remove the document tagged code as it is unused."

pdfium.gyp

Index: pdfium.gyp
diff --git a/pdfium.gyp b/pdfium.gyp
index 87c4fc6b4a238455927fd98228d8468bed6f4c06..658d2dde746e384827689b321ea33593ec79b48f 100644
--- a/pdfium.gyp
+++ b/pdfium.gyp
@@ -253,6 +253,7 @@
         'core/fpdfdoc/csection.h',
         'core/fpdfdoc/ctypeset.cpp',
         'core/fpdfdoc/ctypeset.h',
+        'core/fpdfdoc/doc_tagged.cpp',
         'core/fpdfdoc/include/cpdf_aaction.h',
         'core/fpdfdoc/include/cpdf_action.h',
         'core/fpdfdoc/include/cpdf_actionfields.h',
@@ -282,9 +283,11 @@
         'core/fpdfdoc/include/cpvt_wordplace.h',
         'core/fpdfdoc/include/cpvt_wordprops.h',
         'core/fpdfdoc/include/cpvt_wordrange.h',
+        'core/fpdfdoc/include/fpdf_tagged.h',
         'core/fpdfdoc/include/ipvt_fontmap.h',
         'core/fpdfdoc/include/ipdf_formnotify.h',
         'core/fpdfdoc/ipdf_formnotify.cpp',
+        'core/fpdfdoc/tagged_int.h',
       ],
     },
     {