Why is chrome.runtime undefined in script content?

I have a very simple chrome extension where I am trying to pass a message from a background script to a content script. But chrome.runtime

- undefined.

This is literally all the code here, as you can see almost nothing there. In the content script, the execution time is undefined.

Script background:

chrome.browserAction.onClicked.addListener(function(tab) {
  chrome.runtime.sendMessage({action: 'someAction'}, 
    function(response) {
      console.log('Response: ', response);
    });
});

      

        
        
        
      

    

Script content:

chrome.runtime.onMessage.addListener(function(request, sender, sendResponse) {
  sendResponse({
    user: 'user'
  });
});

      

        
        
        
      

    

manifest.json

{
  "manifest_version": 2,
  "name": "My Extension",
  "version": "1.0",

  "description": "Some stupid extension",

  "browser_action": {
    "default_icon": "icons/MyExtensionIcon.png"
  },
  "icons": {
    "48": "icons/MyExtensionIcon.png"
  },
  "permissions": [
    "tabs",
    "storage",
    "https://*/",
    "http://*/"
  ],
  "content_scripts": [
    {
      "matches": ["*://*.twitter.com/*", "https://twitter.com/*"],
      "js": ["js/content.js"]
    }
  ],
  "background": {
    "scripts": ["js/background.js"],
    "persistent": true
  },
  "web_accessible_resources": [
    "js/*",
    "css/*"
  ]
}

      

        
        
        
      

    

Additional Information:

• Chrome version 58.0.3029.110 (64-bit)
• Installing my extension as "Unpacked extension" with developer mode