API: rename FPDFPage_CountObject() to FPDFPage_CountObjects()

Keep the old name, but mark it as deprecated and don't use it in own
code.

Change-Id: I17b88dccacf494a03562c0d003cfcb2bc03bf430
Reviewed-on: https://pdfium-review.googlesource.com/14750
Reviewed-by: dsinclair <dsinclair@chromium.org>
Commit-Queue: dsinclair <dsinclair@chromium.org>
diff --git a/samples/pdfium_test.cc b/samples/pdfium_test.cc
index 40f12a3..0c002a8 100644
--- a/samples/pdfium_test.cc
+++ b/samples/pdfium_test.cc
@@ -1136,7 +1136,7 @@
 }
 
 void SaveImages(FPDF_PAGE page, const char* pdf_name, int page_num) {
-  for (int i = 0; i < FPDFPage_CountObject(page); ++i) {
+  for (int i = 0; i < FPDFPage_CountObjects(page); ++i) {
     FPDF_PAGEOBJECT obj = FPDFPage_GetObject(page, i);
     if (FPDFPageObj_GetType(obj) != FPDF_PAGEOBJ_IMAGE)
       continue;