Do IWYU for pdfium_test_dump_helper.cc.

Fix the gcc build by adding a missing include for ULONG_MAX.

Change-Id: Idb5089ec4259dbba8fe1e5d693dd494491cf1bea
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/92511
Reviewed-by: Nigi <nigi@chromium.org>
Commit-Queue: Nigi <nigi@chromium.org>
diff --git a/samples/pdfium_test_dump_helper.cc b/samples/pdfium_test_dump_helper.cc
index 3f43a7f..0be3f0d 100644
--- a/samples/pdfium_test_dump_helper.cc
+++ b/samples/pdfium_test_dump_helper.cc
@@ -4,6 +4,7 @@
 
 #include "samples/pdfium_test_dump_helper.h"
 
+#include <limits.h>
 #include <string.h>
 
 #include <algorithm>