Add a type field on the userPromptClosed event

index.bs

@@ -4544,6 +4544,7 @@ failed</dfn> steps given |context| and |navigation status|:
         browsingContext.UserPromptClosedParameters = {
           context: browsingContext.BrowsingContext,
           accepted: bool,
+          type: "alert" / "confirm" / "prompt" / "beforeunload",
           ? userText: text
         }
       </pre>
@@ -4552,7 +4553,7 @@ failed</dfn> steps given |context| and |navigation status|:
 
 <div algorithm>
 The [=remote end event trigger=] is the <dfn export>WebDriver BiDi user prompt
-closed</dfn> steps given |window|, |accepted| and optional |user text|
+closed</dfn> steps given |window|, |type|, |accepted| and optional |user text|
 (default: null).
 
 1. Let |context| be |window|'s [=/browsing context=].
@@ -4562,8 +4563,9 @@ closed</dfn> steps given |window|, |accepted| and optional |user text|
 1. Let |params| be a [=/map=] matching the
    <code>browsingContext.UserPromptClosedParameters</code> production with the
    <code>context</code> field set to |context id|, the <code>accepted</code>
-   field set to |accepted|, and the <code>userText</code> field set to |user
-   text| if |user text| is not null or omitted otherwise.
+   field set to |accepted|, the <code>type</code> field set to |type|, and the
+   <code>userText</code> field set to |user text| if |user text| is not null or
+   omitted otherwise.
 
 1. Let |body| be a [=/map=] matching the
    <code>BrowsingContextUserPromptClosedEvent</code> production, with the