Clarify GraphicsContext::beginLayer()/endLayer() have unexpected behaviors.

Source/core/rendering/svg/RenderSVGResourceClipper.cpp

 /*
  * Copyright (C) 2004, 2005, 2007, 2008 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Rob Buis <buis@kde.org>
  * Copyright (C) Research In Motion Limited 2009-2010. All rights reserved.
  * Copyright (C) 2011 Dirk Schulze <krit@webkit.org>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 167 matching lines @@
         // clipPath can also be clipped by another clipPath.
         SVGResources* resources = SVGResourcesCache::cachedResourcesForRenderObject(this);
         RenderSVGResourceClipper* clipPathClipper = resources ? resources->clipper() : 0;
         ClipperState clipPathClipperState = ClipperNotApplied;
         if (clipPathClipper && !clipPathClipper->applyClippingToContext(this, targetBoundingBox, paintInvalidationRect, context, clipPathClipperState)) {
             // FIXME: Awkward state micro-management. Ideally, GraphicsContextStateSaver should
             //   a) pop saveLayers also
             //   b) pop multiple states if needed (similarly to SkCanvas::restoreToCount())
             // Then we should be able to replace this mess with a single, top-level GCSS.
             maskContentSaver.restore();
-            context->restoreLayer();
+            context->endLayer();
             return false;
         }
 
         drawClipMaskContent(context, targetBoundingBox);
 
         if (clipPathClipper)
             clipPathClipper->postApplyStatefulResource(this, context, clipPathClipperState);
     }
 
     // Masked content layer start.
@@ skipping 159 matching lines @@
         AffineTransform transform;
         transform.translate(objectBoundingBox.x(), objectBoundingBox.y());
         transform.scaleNonUniform(objectBoundingBox.width(), objectBoundingBox.height());
         return transform.mapRect(m_clipBoundaries);
     }
 
     return m_clipBoundaries;
 }
 
 }