Add public method FPDFText_GetTextIndexFromCharIndex

BUG=pdfium:676

Change-Id: I46de35a86769dc2f7f73ac3552306356ca3289a5
Reviewed-on: https://pdfium-review.googlesource.com/2955
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Nicolás Peña <npm@chromium.org>
diff --git a/fpdfsdk/fpdfview_c_api_test.c b/fpdfsdk/fpdfview_c_api_test.c
index c603f59..df3ef19 100644
--- a/fpdfsdk/fpdfview_c_api_test.c
+++ b/fpdfsdk/fpdfview_c_api_test.c
@@ -168,6 +168,7 @@
 
     // fpdf_searchex.h
     CHK(FPDFText_GetCharIndexFromTextIndex);
+    CHK(FPDFText_GetTextIndexFromCharIndex);
 
     // fpdf_structtree.h
     CHK(FPDF_StructTree_GetForPage);