Send port-closed notification when a frame with ports unloads....

chrome/renderer/resources/renderer_extension_bindings.js

 // Copyright (c) 2009 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // -----------------------------------------------------------------------------
 // NOTE: If you change this file you need to touch renderer_resources.grd to
 // have your change take effect.
 // -----------------------------------------------------------------------------
 
 var chrome = chrome || {};
 (function () {
   native function OpenChannelToExtension(id);
+  native function CloseChannel(portId);
   native function PostMessage(portId, msg);
 
   // Port object.  Represents a connection to another script context through
   // which messages can be passed.
   chrome.Port = function(portId) {
     if (chrome.Port.ports_[portId]) {
       throw new Error("Port '" + portId + "' already exists.");
     }
     this.portId_ = portId;  // TODO(mpcomplete): readonly
     this.onDisconnect = new chrome.Event();
@@ skipping 36 matching lines @@
 
   // Sends a message asynchronously to the context on the other end of this
   // port.
   chrome.Port.prototype.postMessage = function(msg) {
     // JSON.stringify doesn't support a root object which is undefined.
     if (msg === undefined)
       msg = null;
     PostMessage(this.portId_, JSON.stringify(msg));
   };
 
+  // Disconnects the port from the other end.
+  chrome.Port.prototype.disconnect = function() {
+    delete chrome.Port.ports_[this.portId_];
+    CloseChannel(this.portId_);
+  }
+
   // Extension object.
   chrome.Extension = function(id) {
     this.id_ = id;
   };
 
   // Opens a message channel to the extension.  Returns a Port for
   // message passing.
   chrome.Extension.prototype.connect = function() {
     var portId = OpenChannelToExtension(this.id_);
     if (portId == -1)
       throw new Error("No such extension: '" + this.id_ + "'");
     return new chrome.Port(portId);
   };
 
   // Returns a resource URL that can be used to fetch a resource from this
   // extension.
   chrome.Extension.prototype.getURL = function(path) {
     return "chrome-extension://" + this.id_ + "/" + path;
   };
+
+  chrome.onUnload_.addListener(function() {
+    for (var i in chrome.Port.ports_) {
+      chrome.Port.ports_[i].disconnect();
+    }
+  });
 })();