Bug 1635818 - Fix some conic gradient WPT accidentally passing when conic gradients are unsupported. r=emilio

Differential Revision: https://phabricator.services.mozilla.com/D74070

testing/web-platform/tests/css/css-images/multiple-position-color-stop-conic-2.html

@@ -4,4 +4,4 @@
 <link rel="help" href="https://drafts.csswg.org/css-images-4/#color-stop-syntax">
 <meta name="assert" content="Color stops with two positions are equivalent to two color stops with the same color">
 <link rel="match" href="multiple-position-color-stop-conic-2-ref.html">
-<div style="background: conic-gradient(red 0% 25%, blue 25% 75%, green 75% 100%); width: 100px; height: 100px;"><br></div>
+<div style="background-image: conic-gradient(red 0% 25%, blue 25% 75%, green 75% 100%); background-color: orange; width: 100px; height: 100px;"><br></div>

testing/web-platform/tests/css/css-images/repeating-conic-gradient.html

@@ -8,6 +8,7 @@
   #gradient {
     width: 200px;
     height: 200px;
+    background-color: red;
     background-image: repeating-conic-gradient(black 0 25%, white 25% 50%);
   }
 </style>

testing/web-platform/tests/css/css-images/tiled-conic-gradients.html

@@ -8,6 +8,7 @@
   #gradient {
     width: 200px;
     height: 200px;
+    background-color: red;
     background-size: 20% 20%;
     background-image: conic-gradient(black 0 25%, white 0 50%, black 0 75%, white 0);
   }