old_contents: console.warn('panel.js');
  
  const messagesEl = document.getElementById('messages');
  
  // chrome.devtools.network.onRequestFinished.addListener((req) => {
  //     const url = req.request.url;
  //     if (url.indexOf('twitter') !== -1) {
  //         console.log(`req:${JSON.stringify(req)}`);
  //         document.getElementById('message').innerText = 'このサイトから、Twitterの香りがするでゲソ';
  //     }
  // });
  
  chrome.devtools.network.onNavigated.addListener((url) => {
      console.clear();
      messagesEl.textContent = '';
  });
  
  // b-5. dump message
  function notifyBackgroundMessage(message) {
      console.warn('from devtools.js to panel.js', message);
      const messageEl = document.createElement('p');
      messageEl.textContent = JSON.stringify(message);
      messagesEl.appendChild(messageEl);
  }
new_contents: console.warn('panel.js');
  
  const messagesEl = document.getElementById('messages');
  
  chrome.devtools.network.onNavigated.addListener((url) => {
      console.clear();
      messagesEl.textContent = '';
  });
  
  // b-5. dump message
  function notifyBackgroundMessage(message) {
      console.warn('from devtools.js to panel.js', message);
      const messageEl = document.createElement('p');
      messageEl.textContent = JSON.stringify(message);
      messagesEl.appendChild(messageEl);
  }
subject: Update sample of google chrome developer tools