old_contents: window.addEventListener('message', function(event) {
    if (event.data === 'debugger-client') {
      var port = event.ports[0];
      listenToPort(port);
    } else if (event.data.type) {
      chrome.extension.sendMessage(event.data);
    }
  });
  
  function listenToPort(port) {
    port.addEventListener('message', function(event) {
      chrome.extension.sendMessage(event.data);
    });
  
    chrome.extension.onMessage.addListener(function(message) {
      if (message.from === 'devtools') {
        port.postMessage(message);
      }
    });
  
    port.start();
  }
  
  // let ember-debug know that content script has executed
  document.documentElement.dataset.emberExtension = 1;
  
new_contents: window.addEventListener('message', function(event) {
    if (event.data === 'debugger-client') {
      var port = event.ports[0];
      listenToPort(port);
    } else if (event.data.type) {
      chrome.extension.sendMessage(event.data);
    }
  });
  
  function listenToPort(port) {
    port.addEventListener('message', function(event) {
      chrome.extension.sendMessage(event.data);
    });
  
    chrome.extension.onMessage.addListener(function(message) {
      if (message.from === 'devtools') {
        port.postMessage(message);
      }
    });
  
    port.start();
  }
  
  // let ember-debug know that content script has executed
  document.documentElement.dataset.emberExtension = 1;
  
  // Allow older versions of Ember (< 1.4) to detect the extension.
  if (document.body) {
    document.body.dataset.emberExtension = 1;
  }
  
subject: Allow Ember to detect the extension