Mark as expected failure a reftest that uses 'direction'.

That property is behind the new --experimental flag.

src/test/harness/reftest/reftest.rs

@@ -82,8 +82,8 @@ fn parse_lists(file: &String, servo_args: &[String]) -> Vec<TestDescAndFn> {
        };
 
     for line in contents.as_slice().lines() {
-       // ignore comments
-       if line.starts_with("#") {
+       // ignore comments or empty lines
+       if line.starts_with("#") || line.is_empty() {
           continue;
        }
 

src/test/ref/basic.list

@@ -75,7 +75,10 @@
 == pseudo_element_a.html pseudo_element_b.html
 == linebreak_simple_a.html linebreak_simple_b.html
 == linebreak_inline_span_a.html linebreak_inline_span_b.html
-== overconstrained_block.html overconstrained_block_ref.html
+
+# Should be == with expected failure. See #2797
+!= overconstrained_block.html overconstrained_block_ref.html
+
 == overflow_auto.html overflow_simple_b.html
 == overflow_scroll.html overflow_simple_b.html
 == overflow_simple_a.html overflow_simple_b.html