Reject connection attempts without prompt if target app doesn't handle the event anyway.

extensions/common/api/runtime.json

 // Copyright 2014 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: Many of these functions and events are implemented by hand and should
 // not elicit any code generation from the schema compiler. These items are
 // marked "nocompile."
 [
   {
     "namespace": "runtime",
@@ skipping 406 matching lines @@
         },
         "description": "Fired when a connection is made from either an extension process or a content script.",
         "parameters": [
           {"$ref": "Port", "name": "port"}
         ]
       },
       {
         "name": "onConnectExternal",
         "type": "function",
         "nocompile": true,
-        "options": {
-          "unmanaged": true
-        },
         "description": "Fired when a connection is made from another extension.",
         "parameters": [
           {"$ref": "Port", "name": "port"}
         ]
       },
       {
         "name": "onMessage",
         "type": "function",
+        "nocompile": true,
         "options": {
           "unmanaged": true
         },
-        "nocompile": true,
         "description": "Fired when a message is sent from either an extension process or a content script.",
         "parameters": [
           {"name": "message", "type": "any", "optional": true, "description": "The message sent by the calling script."},
           {"name": "sender", "$ref": "MessageSender" },
           {"name": "sendResponse", "type": "function", "description": "Function to call (at most once) when you have a response. The argument should be any JSON-ifiable object. If you have more than one <code>onMessage</code> listener in the same document, then only one may send a response. This function becomes invalid when the event listener returns, unless you return true from the event listener to indicate you wish to send a response asynchronously (this will keep the message channel open to the other end until <code>sendResponse</code> is called)." }
         ],
         "returns": {
           "type": "boolean",
           "optional": true,
           "description": "Return true from the event listener if you wish to call <code>sendResponse</code> after the event listener returns."
         }
       },
       {
         "name": "onMessageExternal",
         "type": "function",
-        "options": {
-          "unmanaged": true
-        },
         "nocompile": true,
         "description": "Fired when a message is sent from another extension/app. Cannot be used in a content script.",
         "parameters": [
           {"name": "message", "type": "any", "optional": true, "description": "The message sent by the calling script."},
           {"name": "sender", "$ref": "MessageSender" },
           {"name": "sendResponse", "type": "function", "description": "Function to call (at most once) when you have a response. The argument should be any JSON-ifiable object. If you have more than one <code>onMessage</code> listener in the same document, then only one may send a response. This function becomes invalid when the event listener returns, unless you return true from the event listener to indicate you wish to send a response asynchronously (this will keep the message channel open to the other end until <code>sendResponse</code> is called)." }
         ],
         "returns": {
           "type": "boolean",
           "optional": true,
           "description": "Return true from the event listener if you wish to call <code>sendResponse</code> after the event listener returns."
         }
       },
       {
         "name": "onRestartRequired",
         "type": "function",
         "description": "Fired when an app or the device that it runs on needs to be restarted. The app should close all its windows at its earliest convenient time to let the restart to happen. If the app does nothing, a restart will be enforced after a 24-hour grace period has passed. Currently, this event is only fired for Chrome OS kiosk apps.",
         "parameters": [
           {
             "type": "string",
             "name": "reason",
             "description": "The reason that the event is being dispatched. 'app_update' is used when the restart is needed because the application is updated to a newer version. 'os_update' is used when the restart is needed because the browser/OS is updated to a newer version. 'periodic' is used when the system runs for more than the permitted uptime set in the enterprise policy.",
             "enum": ["app_update", "os_update", "periodic"]
           }
         ]
       }
     ]
   }
 ]