Replaced sequence with FrozenArray in Resize Observer spec

See:
- microsoft#847 (comment)
- microsoft#847 (comment)
- w3c/webidl2.js#392 (comment)

Author: timocov

inputfiles/idl/Resize Observer.widl

@@ -20,9 +20,9 @@ callback ResizeObserverCallback = void (FrozenArray<ResizeObserverEntry> entries
 interface ResizeObserverEntry {
     readonly attribute Element target;
     readonly attribute DOMRectReadOnly contentRect;
-    readonly attribute sequence<ResizeObserverSize> borderBoxSize;
-    readonly attribute sequence<ResizeObserverSize> contentBoxSize;
-    readonly attribute sequence<ResizeObserverSize> devicePixelContentBoxSize;
+    readonly attribute FrozenArray<ResizeObserverSize> borderBoxSize;
+    readonly attribute FrozenArray<ResizeObserverSize> contentBoxSize;
+    readonly attribute FrozenArray<ResizeObserverSize> devicePixelContentBoxSize;
 };
 
 interface ResizeObserverSize {
@@ -35,5 +35,5 @@ interface ResizeObserverSize {
 interface ResizeObservation {
     readonly attribute Element target;
     readonly attribute ResizeObserverBoxOptions observedBox;
-    readonly attribute sequence<ResizeObserverSize> lastReportedSizes;
+    readonly attribute FrozenArray<ResizeObserverSize> lastReportedSizes;
 };