Synchronous XMLHttpRequest on the main thread is deprecated because of its detrimental effects to the end user's experience.

I get the following error in chrome when loadSource is called:

```
Synchronous XMLHttpRequest on the main thread is deprecated because of its detrimental effects to the end user's experience. For more help, check http://xhr.spec.whatwg.org/.
```

``` javascript
function loadSource(url) {
if (typeof url !== 'string') {
return [];
}

if (!TraceKit.remoteFetching) { //Only attempt request if remoteFetching is on.
return '';
}
try {
var getXHR = function() {
try {
return new window.XMLHttpRequest();
} catch (e) {
// explicitly bubble up the exception if not found
return new window.ActiveXObject('Microsoft.XMLHTTP');
}
};

var request = getXHR();
request.open('GET', url, false);
request.send('');
return request.responseText;
} catch (e) {
return '';
}
}
```

Start by tracing loadSource and its callers, then reproduce the warning in Chrome with remoteFetching enabled. Determine how source loading can avoid the synchronous XMLHttpRequest while preserving the existing behavior; done means the deprecation warning no longer occurs and remote source loading still works.

Written by the indexing model from the issue text.