Remove the concept of user stylesheets.

LayoutTests/fast/loader/user-stylesheet-fast-path.html

-<p>
-    This tests that when the user style sheet location is set to a data:
-    URL with base64-encoded UTF-8 data, the style sheet is processed
-    synchronously, instead of invoking the asynchronous loader.
-</p>
-<script>
-    var testObjects = [
-        {result:true,  size:"100px", url:"data:text/css;charset=utf-8;base64,Ym9keSB7Zm9udC1zaXplOiAxMDBweH0="},
-        {result:true,  size:"110px", url:encodeURI("data:text/css;charset=utf-8;base64,                       Ym9keSB7Zm9udC1zaXplOiAxMTBweH0=                  ")},
-        {result:true,  size:"120px", url:encodeURI("data:text/css;charset=utf-8;base64,\n \r \t Ym9k \t eSB7 \r Zm9ud \n \n C1zaXp \r lOiAxM \t jBweH0= \t \r \n")},
-        {result:true,  size:"130px", url:encodeURI("data:text/css;charset=utf-8;base64,\u0059 \u006D \u0039 \u006B eSB7Zm9ud C1zaXplOiAxMzBwe \u0048 \u0030 \u003D")},
-        {result:false, size:"140px", url:"data:text/css;charset=utf-8;base64,Ym9k$#eSB7Zm#9ud(C1zaXp)lOiAxNDBweH0="},
-        {result:false, size:"150px", url:"data:text/css;charset=utf-8;base64,Ym9ke%00SB7Z%20m9udC1z\n\taXplO#iAx%03NTBw%eH0="},
-        {result:false, size:"160px", url:"%50%30%10%00%20%40"}
-    ];
-
-    if (window.testRunner) {
-        testRunner.dumpAsText();
-        testRunner.setUserStyleSheetEnabled(true);
-
-        for (var i = 0; i < testObjects.length; i++) {
-            var obj = testObjects[i];
-            testRunner.setUserStyleSheetLocation(obj.url);
-
-            document.body.offsetTop;
-            var result = getComputedStyle(document.body).fontSize == obj.size;
-            document.write((result == obj.result ? "PASS" : "FAIL") + " " + obj.size + "<br>");
-
-            testRunner.setUserStyleSheetLocation("");
-        }
-    } else
-        document.write("This test can only be run in DumpRenderTree.");
-</script>