Element no longer works in IE11 due to URL API usage

Description

After upgrading to Polymer 2 and webcomponents v1, iron-component-page no longer works in IE11.

It fails in the _srcChanged function on the use of the URL api:

} else if (this.src) {
    srcUrl = new URL(this.src, this.base).toString();
} else {
    var base = _baseUrl(this.base);
    srcUrl = new URL(base.match(/([^\/]*)\/$/)[1] + ".html", base).toString();
}

IE11 does not support this API. Checking the source history I noticed the element has used this API since it's creation, which made me wonder how my app previously worked in Polymer 1.x.

I believe the URL api was previously polyfilled in the webcomponents.js suite. It no longer appears to be in the new v1 polyfills.

Steps to reproduce

The following code sample demonstrates the lack of availability of the URL api in IE11 after loading the polyfills.

<!doctype html>
<html>
<head>
</head>
<body>
    <script src="/bower_components/webcomponentsjs/webcomponents-loader.js"></script>
    <link rel="import" href="/bower_components/polymer/polymer.html">
    <script>
        var x = new URL('http://helloworld.com');
        console.log(x);
    </script>
</body>
</html>

Browsers Affected

[ ] Chrome
[ ] Firefox
[ ] Safari 9
[ ] Safari 8
[ ] Safari 7
[ ] Edge
[ X ] IE 11
[ X ] IE 10

PolymerElements / iron-component-page