Can Polymer extend Electron's webview component? - polymer

Question

In Electron (Atom-Shell), I'm trying to use Polymer 0.5 to extend Electron's webview tag (to add some custom attributes while retaining all of webview's methods). But I'm getting a NotSupportedError when I try to use my custom component. Is there a way to make this work?
Here's how I'm extending the webview:
<polymer-element name="my-webview" extends="webview">
<script>
Polymer({
// I'll add some custom attributes later
});
</script>
</polymer-element>
But when I try to use my-webview (either of these ways):
<my-webview src="http://example.com"></my-webview>
<webview is="my-webview" src="http://example.com"></webview>
...I get this error:
Uncaught NotSupportedError: Failed to execute 'registerElement' on
'Document': Registration failed for type 'my-webview'. The tag name
specified in 'extends' is a custom element name. Use inheritance
instead.
Now, it's true that Electron's webview is indeed a custom element. But Polymer happily extends other custom elements, right?
It seems like one problem might be that "webview" doesn't have a '-' in its name, so Polymer's findTypeExtension doesn't realize it's a custom element.
Is there any way to work around this and convince Polymer that webview needs to be extended through inheritance, like other custom elements?