Add support for asynchronously loading modules from the background page.

extensions/renderer/resources/serial_custom_bindings.js

Index: extensions/renderer/resources/serial_custom_bindings.js
diff --git a/extensions/renderer/resources/serial_custom_bindings.js b/extensions/renderer/resources/serial_custom_bindings.js
index 31f6daec467a7a6e59a9692e57d26d0088ff8f0f..c0e2738eb080477a0580bfbf877970a520ce2ac2 100644
--- a/extensions/renderer/resources/serial_custom_bindings.js
+++ b/extensions/renderer/resources/serial_custom_bindings.js
@@ -12,21 +12,10 @@
  */
 
 var binding = require('binding').Binding.create('serial');
+var utils = require('utils');
 
-function createAsyncProxy(targetPromise, functionNames) {
-  var functionProxies = {};
-  $Array.forEach(functionNames, function(name) {
-    functionProxies[name] = function() {
-      var args = arguments;
-      return targetPromise.then(function(target) {
-        return $Function.apply(target[name], target, args);
-      });
-    };
-  });
-  return functionProxies;
-}
-
-var serialService = createAsyncProxy(requireAsync('serial_service'), [
+var serialService = utils.createAsyncProxy(
+    utils.requireAsyncFromBackgroundPage('serial_service'), [
   'getDevices',
   'createConnection',
   'getConnection',