From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Jeremy Apthorp <nornagon@nornagon.net>
Date: Wed, 4 Mar 2020 11:18:03 -0800
Subject: feat: add onclose to MessagePort

This adds the 'onclose' event to MessagePort. This is
[proposed](https://github.com/w3ctag/design-reviews/issues/269#issuecomment-407584290)
in w3c and has been discussed for years without conclusion. I'd like to
get this standardised, but in lieu of that, this makes MessagePort a
whole bunch more useful!

diff --git a/third_party/blink/renderer/core/messaging/message_port.cc b/third_party/blink/renderer/core/messaging/message_port.cc
index 5d7780c48a74fc7d95aeb690c90ab394b1e01a83..15f5f0f6aa05d3b17adae87286c92df9cc26a712 100644
--- a/third_party/blink/renderer/core/messaging/message_port.cc
+++ b/third_party/blink/renderer/core/messaging/message_port.cc
@@ -195,6 +195,7 @@ void MessagePort::close() {
     Entangle(pipe.TakePort0(), nullptr);
   }
   closed_ = true;
+  DispatchEvent(*Event::Create(event_type_names::kClose));
 }
 
 void MessagePort::Entangle(MessagePortDescriptor port_descriptor,
diff --git a/third_party/blink/renderer/core/messaging/message_port.h b/third_party/blink/renderer/core/messaging/message_port.h
index 3678c9887c1596f813cd9618b1e9728808659fa8..5fc9edb82bf983fee9084d89904e232ecfe66fd9 100644
--- a/third_party/blink/renderer/core/messaging/message_port.h
+++ b/third_party/blink/renderer/core/messaging/message_port.h
@@ -125,6 +125,13 @@ class CORE_EXPORT MessagePort : public EventTarget,
     return GetAttributeEventListener(event_type_names::kMessageerror);
   }
 
+  void setOnclose(EventListener* listener) {
+    SetAttributeEventListener(event_type_names::kClose, listener);
+  }
+  EventListener* onclose() {
+    return GetAttributeEventListener(event_type_names::kClose);
+  }
+
   // A port starts out its life entangled, and remains entangled until it is
   // closed or is cloned.
   bool IsEntangled() const { return !closed_ && !IsNeutered(); }
diff --git a/third_party/blink/renderer/core/messaging/message_port.idl b/third_party/blink/renderer/core/messaging/message_port.idl
index 6fab27fcdf1c333739b6ffe88b3cc4eed3301ee4..3f1f181d9b8a66997136f870f55c97c08294b6eb 100644
--- a/third_party/blink/renderer/core/messaging/message_port.idl
+++ b/third_party/blink/renderer/core/messaging/message_port.idl
@@ -40,4 +40,5 @@
     // event handlers
     attribute EventHandler onmessage;
     attribute EventHandler onmessageerror;
+    attribute EventHandler onclose;
 };