Remove the concept of user stylesheets.

Source/core/testing/Internals.idl

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  * Copyright (C) 2013 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 178 matching lines @@
     [RaisesException] ClientRectList nonFastScrollableRects(Document document);
 
     [RaisesException] DOMString repaintRectsAsText(Document document);
     [RaisesException] ClientRectList repaintRects(Element element);
 
     [RaisesException] void garbageCollectDocumentResources(Document document);
     void evictAllResources();
 
     void allowRoundingHacks();
 
-    void insertAuthorCSS(Document document, DOMString css);
-    void insertUserCSS(Document document, DOMString css);
-
     unsigned long numberOfLiveNodes();
     unsigned long numberOfLiveDocuments();
     sequence<DOMString> consoleMessageArgumentCounts(Document document);
     Window openDummyInspectorFrontend(DOMString url);
     void closeDummyInspectorFrontend();
     unsigned long[] setMemoryCacheCapacities(unsigned long minDeadBytes, unsigned long maxDeadBytes, unsigned long totalBytes);
     [RaisesException] void setInspectorResourcesDataSizeLimits(long maximumResourcesContentSize, long maximumSingleResourceContentSize);
 
     DOMString counterValue(Element element);
     long pageNumber(Element element, optional float pageWidth, optional float pageHeight);
@@ skipping 44 matching lines @@
     [RaisesException] DOMString getImageSourceURL(Element element);
 
     boolean isSelectPopupVisible(Node node);
 
     [RaisesException] ClientRect selectionBounds();
 
     boolean loseSharedGraphicsContext3D();
 
     [RaisesException] void forceCompositingUpdate(Document document);
 };