Auto merge of #15323 - Manishearth:gradient-stop, r=heycam

Ensure that gradients have at least 2 stops

fixes https://bugzilla.mozilla.org/show_bug.cgi?id=1335656

r? @heycam

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components/style/values/specified/image.rs

@@ -141,6 +141,11 @@ impl Gradient {
             _ => { return Err(()); }
         };
 
+        // https://drafts.csswg.org/css-images/#typedef-color-stop-list
+        if stops.len() < 2 {
+            return Err(())
+        }
+
         Ok(Gradient {
             stops: stops,
             repeating: repeating,