Merge pull request w3c#5450 from autokagami/resize-observer-1

[resize-observer-1] Align with Web IDL specification

Author: tabatkins

resize-observer-1/Overview.bs

@@ -191,9 +191,9 @@ In this case, author will need to use multiple ResizeObservers.
 [Exposed=(Window)]
 interface ResizeObserver {
     constructor(ResizeObserverCallback callback);
-    void observe(Element target, optional ResizeObserverOptions options);
-    void unobserve(Element target);
-    void disconnect();
+    undefined observe(Element target, optional ResizeObserverOptions options = {});
+    undefined unobserve(Element target);
+    undefined disconnect();
 };
 </pre>
 
@@ -239,7 +239,7 @@ interface ResizeObserver {
 <h3 id="resize-observer-callback">ResizeObserverCallback</h3>
 
 <pre class="idl">
-callback ResizeObserverCallback = void (sequence&lt;ResizeObserverEntry> entries, ResizeObserver observer);
+callback ResizeObserverCallback = undefined (sequence&lt;ResizeObserverEntry> entries, ResizeObserver observer);
 </pre>
 
 This callback delivers {{ResizeObserver}}'s notifications. It is invoked by a
@@ -290,6 +290,7 @@ A future version of this spec will extend the returned {{FrozenArray}} to contai
 </p>
 
 <pre class="idl">
+    [Exposed=Window]
     interface ResizeObserverSize {
         readonly attribute unrestricted double inlineSize;
         readonly attribute unrestricted double blockSize;