Fix BUG=skia:5662

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4661

Change-Id: I5f5b10387be5d538347a3626c165cc17af154212
Reviewed-on: https://skia-review.googlesource.com/4661
Reviewed-by: Hal Canary <halcanary@google.com>
Commit-Queue: Hal Canary <halcanary@google.com>
diff --git a/tests/PDFDocumentTest.cpp b/tests/PDFDocumentTest.cpp
index fb32819..fca8496 100644
--- a/tests/PDFDocumentTest.cpp
+++ b/tests/PDFDocumentTest.cpp
@@ -61,9 +61,9 @@
     }
 
     FILE* file = fopen(path.c_str(), "r");
-    // The created file should be empty.
-    char buffer[100];
-    REPORTER_ASSERT(reporter, fread(buffer, 1, 1, file) == 0);
+    // Test that only the header is written, not the full document.
+    char buffer[256];
+    REPORTER_ASSERT(reporter, fread(buffer, 1, sizeof(buffer), file) < sizeof(buffer));
     fclose(file);
 }