Reviewed by Geoff.

        Fixed for <rdar://problem/5760530> REGRESSION: Assertion failure in 
        Document::removePendingSheet() from r30438

        r30438 added a call to CachedResource::error() from inside 
        Loader::didReceiveData() if a CSS file 4xxs. There was an 
        assumption in the loader, though, that either error() would be 
        called, or didFinishLoading() would be called, so some work is 
        duplicated in each. Now that we are calling an error() on files 
        that will also make it to didFinishLoading() (since they succeeded 
        in the network layer), we need to make sure we do not duplicate the 
        work. CachedCSSStyleSheet::error() calls checkNotify, which ends up 
        decrementing the document's pending style sheet counter. 
        checkNotify() was still getting called, though, through the normal  
        didFinishLoading code path, and the counter was being decremented 
        twice. Bad!

        * loader/loader.cpp:
        (WebCore::Loader::didFinishLoading):
        (WebCore::Loader::didReceiveData):

LayoutTests:

        Reviewed by Geoff.

        Test for <rdar://problem/5760530> REGRESSION: Assertion failure in 
        Document::removePendingSheet() from r30438

        * http/tests/misc/missing-style-sheet-expected.txt: Added.
        * http/tests/misc/missing-style-sheet.html: Added.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@30587 268f45cc-cd09-0410-ab3c-d52691b4dbfc