--- a/testing/web-platform/tests/interfaces/resize-observer.idl
+++ b/testing/web-platform/tests/interfaces/resize-observer.idl
@@ -1,15 +1,15 @@
 // GENERATED CONTENT - DO NOT EDIT
 // Content was automatically extracted by Reffy into reffy-reports
 // (https://github.com/tidoust/reffy-reports)
 // Source: Resize Observer (https://drafts.csswg.org/resize-observer/)
 
 enum ResizeObserverBoxOptions {
-    "border-box", "content-box"
+    "border-box", "content-box", "device-pixel-content-box"
 };
 
 dictionary ResizeObserverOptions {
     ResizeObserverBoxOptions box = "content-box";
 };
 
 [Exposed=(Window),
  Constructor(ResizeObserverCallback callback)]
@@ -22,16 +22,17 @@ interface ResizeObserver {
 callback ResizeObserverCallback = void (sequence<ResizeObserverEntry> entries, ResizeObserver observer);
 
 [Exposed=Window, Constructor(Element target)]
 interface ResizeObserverEntry {
     readonly attribute Element target;
     readonly attribute DOMRectReadOnly contentRect;
     readonly attribute ResizeObserverSize borderBoxSize;
     readonly attribute ResizeObserverSize contentBoxSize;
+    readonly attribute ResizeObserverSize devicePixelContentBoxSize;
 };
 
 interface ResizeObserverSize {
     readonly attribute unrestricted double inlineSize;
     readonly attribute unrestricted double blockSize;
 };
 
 [Constructor(Element target)