Move floated_negative_margins_a.html to wpt reftests.

tests/ref/basic.list

@@ -11,7 +11,6 @@ fragment=top != ../html/acid2.html acid2_ref.html
 
 == acid2_noscroll.html acid2_ref_broken.html
 flaky_cpu == append_style_a.html append_style_b.html
-== floated_negative_margins_a.html floated_negative_margins_ref.html
 == font_size.html font_size_ref.html
 # `?` and `#` in the name is a test for https://github.com/servo/servo/issues/3340
 

tests/wpt/mozilla/meta/MANIFEST.json

@@ -1439,6 +1439,18 @@
             "url": "/_mozilla/css/floated_list_item_a.html"
           }
         ],
+        "css/floated_negative_margins_a.html": [
+          {
+            "path": "css/floated_negative_margins_a.html",
+            "references": [
+              [
+                "/_mozilla/css/floated_negative_margins_ref.html",
+                "=="
+              ]
+            ],
+            "url": "/_mozilla/css/floated_negative_margins_a.html"
+          }
+        ],
         "css/floated_table_with_margin_a.html": [
           {
             "path": "css/floated_table_with_margin_a.html",
@@ -6288,6 +6300,18 @@
           "url": "/_mozilla/css/floated_list_item_a.html"
         }
       ],
+      "css/floated_negative_margins_a.html": [
+        {
+          "path": "css/floated_negative_margins_a.html",
+          "references": [
+            [
+              "/_mozilla/css/floated_negative_margins_ref.html",
+              "=="
+            ]
+          ],
+          "url": "/_mozilla/css/floated_negative_margins_a.html"
+        }
+      ],
       "css/floated_table_with_margin_a.html": [
         {
           "path": "css/floated_table_with_margin_a.html",

tests/wpt/mozilla/tests/css/floated_negative_margins_a.html

@@ -1,3 +1,4 @@
+<link rel=match href=floated_negative_margins_ref.html>
 <style>
 body {
     margin: 0;