title: clear clipboard in chrome
body: <p>In my extension, I'm writing something to clipboard and then pasting it.<br>
  After the job is done, I would like to clear clipboard to prevent possible privacy/security issues (maybe user was dealing with some logins,passwords etc...)<br>
  I could simply write <code>...</code> or <code>abc</code> to clipboard, but it would be much better to simply wipe it.<br>
  Is that possible in Chrom(iums) like clearData in IE?</p>
  
  <p>trying to write empty string to dummy textarea that is used as placeholder won't do good. </p>
  
  <pre><code>txtArea.value = '';
  txtArea.focus();
  txtArea.select();
  document.execCommand('Copy');
  </code></pre>
  
  <p>....nothing is copied to clipboard. Same if I use<br>
   <code>txtArea.value = null;</code></p>