Add APIs for limited use of document tagged code.

fpdfsdk/fpdfview_c_api_test.c

Index: fpdfsdk/fpdfview_c_api_test.c
diff --git a/fpdfsdk/fpdfview_c_api_test.c b/fpdfsdk/fpdfview_c_api_test.c
index 5e6c36f2b1d7c9898f36cf7aa8e7cfcd79d2ae7d..ed9a3fafe274bc43446f9bb952dd7fe2a2bd4fe1 100644
--- a/fpdfsdk/fpdfview_c_api_test.c
+++ b/fpdfsdk/fpdfview_c_api_test.c
@@ -20,6 +20,7 @@
 #include "public/fpdf_progressive.h"
 #include "public/fpdf_save.h"
 #include "public/fpdf_searchex.h"
+#include "public/fpdf_structtree.h"
 #include "public/fpdf_sysfontinfo.h"
 #include "public/fpdf_text.h"
 #include "public/fpdf_transformpage.h"
@@ -154,6 +155,15 @@ int CheckPDFiumCApi() {
     // fpdf_searchex.h
     CHK(FPDFText_GetCharIndexFromTextIndex);
 
+    // fpdf_structtree.h
+    CHK(FPDF_StructTree_GetForPage);
+    CHK(FPDF_StructTree_Close);
+    CHK(FPDF_StructTree_CountChildren);
+    CHK(FPDF_StructTree_GetChildAtIndex);
+    CHK(FPDF_StructElement_GetAltText);
+    CHK(FPDF_StructElement_CountChildren);
+    CHK(FPDF_StructElement_GetChildAtIndex);
+
     // fpdf_sysfontinfo.h
     CHK(FPDF_GetDefaultTTFMap);
     CHK(FPDF_AddInstalledFont);