Bug 827523 (part 2) - DMD: Swap the diff order in test mode. r=jlebar.

--HG--
extra : rebase_source : d8b96799e7353f9d838f31ddb4b1aaca3ab6ca9c

memory/replace/dmd/check_test_output.py

@@ -125,7 +125,7 @@ def main():
 
     print("diffing output to", diff_name)
 
-    ret = subprocess.call(["diff", "-u", filtered_name, expected_name],
+    ret = subprocess.call(["diff", "-u", expected_name, filtered_name],
                           stdout=open(diff_name, "w"))
 
     if ret == 0: