title: Chrome extension: Send message from background script to *all* tabs
body: <p>Is there a way to have the background script inform <em>all</em> currently open tabs (i.e. their content scripts) that an event took place.</p>
  
  <p>Something like the following basically</p>
  
  <pre><code>chrome.tabs.sendMessage("*", {foo: "bar"})
  </code></pre>
  
  <p>I suspect I could maintain a list of open tabs on the background script, if that's possible, and use that. But is there a simpler way?</p>