Call FPDFPage_FormFieldZOrderAtPoint() from embedder test.

Change-Id: Iaba97dc37a127fb969492433e3c2e9b091cd460d
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/62672
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Tom Sepez <tsepez@chromium.org>

fpdfsdk/fpdf_formfill_embeddertest.cpp

diff --git a/fpdfsdk/fpdf_formfill_embeddertest.cpp b/fpdfsdk/fpdf_formfill_embeddertest.cpp
index 7027576..5b56a3c 100644
--- a/fpdfsdk/fpdf_formfill_embeddertest.cpp
+++ b/fpdfsdk/fpdf_formfill_embeddertest.cpp
@@ -914,6 +914,8 @@
     // Click on the textfield
     EXPECT_EQ(FPDF_FORMFIELD_TEXTFIELD,
               FPDFPage_HasFormFieldAtPoint(form_handle(), page, 120.0, 120.0));
+    EXPECT_EQ(
+        0, FPDFPage_FormFieldZOrderAtPoint(form_handle(), page, 120.0, 120.0));
     FORM_OnMouseMove(form_handle(), page, 0, 120.0, 120.0);
     FORM_OnLButtonDown(form_handle(), page, 0, 120.0, 120.0);
     FORM_OnLButtonUp(form_handle(), page, 0, 120.0, 120.0);