title: How to postMessage to webview in Dart google chrome app (securityError)
body: <p>I'm building a Google Chrome App with webview using Dart programming language.
  The app is communicating with webview content via postMessage. If I run the app from DartEditor (run as Chrome app) postMessage works ok. But after build (dart2js) and loading into browser with "Load unpackaged extention..." - application can't get webview contentWindow and execute postMessage on it.</p>
  
  <p>Error from chrome dev console:
  Uncaught SecurityError: Blocked a frame with origin "chrome-extension://bpddihniogcgmnlaghkacfagkecgnljo" from accessing a frame with origin "swappedout://".  The frame requesting access has a protocol of "chrome-extension", the frame being accessed has a protocol of "swappedout". Protocols must match.</p>
  
  <p>Google Chrome Version 36.0.1951.5 dev
  Dart version SDK 1.4.2, version 1.5.0-dev.4.2 - gives same error.</p>
  
  <p>This is minimal working example to demonstrate the problem - <a href="https://github.com/Dumbris/dart_chrome_app_webview_security_error" rel="nofollow">https://github.com/Dumbris/dart_chrome_app_webview_security_error</a></p>