Fix extension bindings injection for iframes

chrome/test/data/extensions/api_test/bindings/external_message_listener/background.js

+// Copyright 2016 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.
+
+var messagesReceived = [];
+
+chrome.runtime.onMessageExternal.addListener(function(msg, sender, respond) {
+  messagesReceived.push({msg:msg, sender:sender});
+  if (msg == "from_sender") {

[Devlin, 2016/07/14 16:46:35]

prefer single quotes in JS

[asargent_no_longer_on_chrome, 2016/07/20 21:36:47]

Done. (Here and elsewhere in the CL)

+    chrome.test.sendMessage("" + messagesReceived.length);
+  }
+});
+
+chrome.test.sendMessage('receiver_ready');