After doing some research, the code that I have come up with is this:
var outUrl; // first get the windowid chrome.windows.getCurrent(function(window) {
Maybe this is what your looking for....
chrome.tabs.query({'active': true, 'windowId': chrome.windows.WINDOW_ID_CURRENT}, function(tabs){ alert(tabs[0].url); } );
And the tabs permission needs to be set in the manifest...
manifest.json
"permissions": [ "tabs" ]