Make @import work in user stylesheets.  The first bug was that the URL wasn't being set on the
user sheets themselves, so relative @import URLs couldn't resolve properly.  The second bug
was that the loads would be denied.  This is fixed by using the requestUserCSSStyleSheet method
instead of the normal request method.  In order to know when to do this, CSSStyleSheets now have
a propagated boolean, m_isUserStyleSheet, that lets them know if they are user stylesheets or not.

Reviewed by Anders Carlsson.

* css/CSSImportRule.cpp:
(WebCore::CSSImportRule::insertedIntoParent):
* css/CSSStyleSheet.cpp:
(WebCore::CSSStyleSheet::CSSStyleSheet):
* css/CSSStyleSheet.h:
(WebCore::CSSStyleSheet::setIsUserStyleSheet):
(WebCore::CSSStyleSheet::isUserStyleSheet):
* dom/Document.cpp:
(WebCore::Document::pageUserSheet):
(WebCore::Document::pageGroupUserSheets):



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@48773 268f45cc-cd09-0410-ab3c-d52691b4dbfc