Test for Bug 11850: Webarchive fails to save images referenced in CSS

This test makes sure that the URL in the shift-jis encoded CSS file is encoded properly in the webarchive.

Expected ?img-src-no-charset-%88%9F query string for <img> tag with no document charset:
Expected ?css-url-no-charset-%88%9F query string for CSS url() with no CSS charset:
Expected ?css-url-shift-jis-%88%9F query string for CSS url() with shift-jis CSS charset:
Expected ?css-url-utf-8-%E4%BA%9C query string for CSS url() with utf-8 CSS charset: