Fix extension bindings injection for iframes

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

Index: chrome/test/data/extensions/api_test/bindings/external_message_listener/background.js
diff --git a/chrome/test/data/extensions/api_test/bindings/external_message_listener/background.js b/chrome/test/data/extensions/api_test/bindings/external_message_listener/background.js
new file mode 100644
index 0000000000000000000000000000000000000000..47036306b72d44ce8dff2783d5fde874bb288bf1
--- /dev/null
+++ b/chrome/test/data/extensions/api_test/bindings/external_message_listener/background.js
@@ -0,0 +1,14 @@
+// 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') {
+    chrome.test.sendMessage('' + messagesReceived.length);
+  }
+});
+
+chrome.test.sendMessage('receiver_ready');