Troubles running Polymer project in Dartium: Invalid URL

I downloaded the Spark project (https://github.com/dart-lang/spark) and tried to run the widget examples.

After adding

<link rel="import" href="../packages/polymer/polymer.html">

to the entry page of the first example to make it work with Polymer 0.9.10-dev.x (I added ../ because the entry page is in a subdirectory in example) I get this error:

 Uncaught SyntaxError: Failed to construct 'URL': Invalid URL (http://127.0.0.1:3030/widgets/example/packages/web_components/platform.js:35)

When I copy this URL to Dartium the script is shown in the browser, so the URL is OK.

Any idea what could cause this error message?

Solution

While trying to add all relevant information to the question I found the cause and a solution:

I changed

<!-- BUG: https://code.google.com/p/dart/issues/detail?id=14382 -->
<!-- link rel="stylesheet" href="xyz.css" -->
<style>
  @import url("../../../packages/spark_widgets/spark_modal/spark_modal.css");
</style>

<link rel="stylesheet" href="spark_modal.css">

and the error message went away and the examples are working fine now.