title: sendMessage from popup to content.js not working in chrome extension
body: <p>I'm trying to make a popup interface for a chrome extension. I can't seem to send a message from the popup.html/popup.js to the content.js script. Here's what I have so far. When I click on the extension icon I get a button that says clickme. I click it and nothing happens, no errors in the chrome javascript console, and no message to content.js. </p>
  
  <p>Manifest</p>
  
  <pre><code>{
  "content_security_policy": "script-src 'self' 'unsafe-eval'; object-src 'self'",
    "manifest_version": 2,
    "name": "extensiontest",
    "version": "0.2",
    "content_scripts": [
    {
      "matches": [
        "&lt;all_urls&gt;"
      ],
      "js": ["content.js"]
    }
  ],
  "browser_action": {
    "default_icon": "Beaker.png",
      "default_popup":"popup.html"
  },
  "background": {
    "scripts": ["background.js"]
  },
  "permissions": [
      "tabs"
    ]
  }
  </code></pre>
  
  <p>popup.html</p>
  
  <pre><code>&lt;html&gt;
  &lt;head&gt;&lt;/head&gt;
  &lt;script src="popup.js"&gt;&lt;/script&gt;
  &lt;body&gt;
  &lt;input id="button1" type=button value=clickme&gt;
  &lt;/body&gt;&lt;/html&gt;
  </code></pre>
  
  <p>popup.js</p>
  
  <pre><code>function popup(){
      alert(1);
        chrome.tabs.query({active: true, currentWindow: true}, function(tabs) {
      var activeTab = tabs[0];
      chrome.tabs.sendMessage(activeTab.id, {"message": "start"});
    });
  
  button1=document.getElementById("button1");
  button1.addEventListener('click', popup)
  }
  </code></pre>
  
  <p>content.js</p>
  
  <pre><code>   chrome.runtime.onMessage.addListener(
        function(request, sender, sendResponse) {
          if( request.message === "start" ) {
           start();
               }
        }
      );
  
      function start(){
          alert("started");
      }
  </code></pre>