Implement externally_connectable! Web pages can now communicate directly with

chrome/renderer/resources/extensions/miscellaneous_bindings.js

 // Copyright (c) 2012 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.
 
 // This contains unprivileged javascript APIs for extensions and apps.  It
 // can be loaded by any extension-related context, such as content scripts or
 // background pages. See user_script_slave.cc for script that is loaded by
 // content scripts only.
 
   // TODO(kalman): factor requiring chrome out of here.
@@ skipping 178 matching lines @@
     if (targetExtensionId != extensionId)
       return false;  // not for us
 
     if (ports[getOppositePortId(portId)])
       return false;  // this channel was opened by us, so ignore it
 
     // Determine whether this is coming from another extension, so we can use
     // the right event.
     var isExternal = sourceExtensionId != extensionId;
 
-    var sender = {id: sourceExtensionId};
+    var sender = {};
+    if (sourceExtensionId != '')
+      sender.id = sourceExtensionId;
     if (sourceUrl)
       sender.url = sourceUrl;
     if (sourceTab)
       sender.tab = sourceTab;
 
     // Special case for sendRequest/onRequest and sendMessage/onMessage.
     if (channelName == kRequestChannel || channelName == kMessageChannel) {
       return dispatchOnRequest(portId, channelName, sender,
                                sourceExtensionId, targetExtensionId, sourceUrl,
                                isExternal);
@@ skipping 113 matching lines @@
 exports.Port = Port;
 exports.createPort = createPort;
 exports.sendMessageImpl = sendMessageImpl;
 exports.sendMessageUpdateArguments = sendMessageUpdateArguments;
 
 // For C++ code to call.
 exports.hasPort = hasPort;
 exports.dispatchOnConnect = dispatchOnConnect;
 exports.dispatchOnDisconnect = dispatchOnDisconnect;
 exports.dispatchOnMessage = dispatchOnMessage;