Bug 1606827 - A corner is not rounded when the radius is zero in eith…

…er dimension (not necessarily both) r=nical

Differential Revision: https://phabricator.services.mozilla.com/D58615

[wrupdater] From https://hg.mozilla.org/mozilla-central/rev/5105e62fbbe6cb144a7a7a756128da326d724004

webrender_api/src/display_item.rs

@@ -1302,12 +1302,14 @@ impl BorderRadius {
         }
     }
 
+    /// Return whether, in each corner, the radius in *either* direction is zero.
+    /// This means that none of the corners are rounded.
     pub fn is_zero(&self) -> bool {
-        if let Some(radius) = self.is_uniform() {
-            radius == 0.0
-        } else {
-            false
-        }
+        let corner_is_zero = |corner: &LayoutSize| corner.width == 0.0 || corner.height == 0.0;
+        corner_is_zero(&self.top_left) &&
+        corner_is_zero(&self.top_right) &&
+        corner_is_zero(&self.bottom_right) &&
+        corner_is_zero(&self.bottom_left)
     }
 }