Added backwards compatibility for Chrome's old messaging API

chrome/common.js

Index: chrome/common.js
===================================================================
--- a/chrome/common.js
+++ b/chrome/common.js
@@ -56,7 +56,7 @@
 
   var MessageEventTarget = function()
   {
-    WrappedEventTarget.call(this, chrome.runtime.onMessage);
+    WrappedEventTarget.call(this, chrome.runtime.onMessage || chrome.extension.onRequest);
   };
   MessageEventTarget.prototype = {
     __proto__: WrappedEventTarget.prototype,
@@ -68,18 +68,13 @@
     }
   };
 
+
   /* API */
 
   ext = {
     backgroundPage: {
-      sendMessage: function(message, responseCallback)
-      {
-        chrome.runtime.sendMessage(message, responseCallback);
-      },
-      getWindow: function()
-      {
-        return chrome.extension.getBackgroundPage();
-      }
+      sendMessage: chrome.runtime.sendMessage || chrome.extension.sendRequest,

[Wladimir Palant, 2013/11/17 06:19:45]

This will error out with "Cannot get property sendMessage of undefined" on
anything older than Chrome 22. You have to check whether chrome.runtime is
actually present.

+      getWindow: chrome.extension.getBackgroundPage
     },
     getURL: chrome.extension.getURL,
     onMessage: new MessageEventTarget(),