title: Obtaining "this" tab ID from content script in Chrome extension?
body: <p>From a content script, is it possible to access that tab's <code>id</code>?</p>
  <p>I want to send a message to the background page from the content script that tells my extension to &quot;do something with this tab&quot; using the <code>chrome.tabs.*</code> API.</p>
  <p>A <code>tabID</code> is needed, and there is no point in doing a bunch of logic in the background page to hunt for a <code>tabID</code> when my content script can simply tell it the <code>tabID</code> in the message contents.</p>