Copy To Clipboard in Google Chrome Extensions using Javascript. Source: http://www.pakzilla.com/2012/03/20/how-to-copy-to-clipboard-in-chrome-extension/

Copy To Clipboard in Google Chrome Extensions using Javascript

function copyToClipboard( text ){
                var copyDiv = document.createElement('div');
                copyDiv.contentEditable = true;
                document.body.appendChild(copyDiv);
                copyDiv.innerHTML = text;
                copyDiv.unselectable = "off";
                copyDiv.focus();
                document.execCommand('SelectAll');
                document.execCommand("Copy", false, null);
                document.body.removeChild(copyDiv);