Fix positioning of CSS reference clips in composited layers.

third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/paint/PaintLayerPainter.h"
 
 #include "core/frame/FrameView.h"
 #include "core/frame/Settings.h"
 #include "core/layout/ClipPathOperation.h"
 #include "core/layout/LayoutBlock.h"
@@ skipping 142 matching lines @@
             Document& document = paintLayer.layoutObject()->document();
             // FIXME: It doesn't work with forward or external SVG references (https://bugs.webkit.org/show_bug.cgi?id=90405)
             Element* element = document.getElementById(referenceClipPathOperation->fragment());
             if (isSVGClipPathElement(element) && element->layoutObject()) {
                 if (!rootRelativeBoundsComputed) {
                     rootRelativeBounds = paintLayer.physicalBoundingBoxIncludingReflectionAndStackingChildren(offsetFromRoot);
                     rootRelativeBoundsComputed = true;
                 }
 
                 m_resourceClipper = toLayoutSVGResourceClipper(toLayoutSVGResourceContainer(element->layoutObject()));
+                // When SVG applies the clip and the coordinate system is "user space on use", we must explicitly pass in
+                // the layer offset to have the clip paint in the correct location. When the coordinate system is
+                // "object bounding box" the offset is already accounted for in the rootRelativeBounds.
+                FloatPoint layerPositionOffset = m_resourceClipper->clipPathUnits() == SVGUnitTypes::SVG_UNIT_TYPE_USERSPACEONUSE ?
+                    FloatPoint(offsetFromRoot) : FloatPoint();
                 if (!SVGClipPainter(*m_resourceClipper).prepareEffect(*paintLayer.layoutObject(), FloatRect(rootRelativeBounds),
-                    FloatRect(rootRelativeBounds), context, m_clipperState)) {
+                    FloatRect(rootRelativeBounds), layerPositionOffset, context, m_clipperState)) {
                     // No need to post-apply the clipper if this failed.
                     m_resourceClipper = 0;
                 }
             }
         }
     }
 
     ~ClipPathHelper()
     {
         if (m_resourceClipper)
@@ skipping 629 matching lines @@
     if (!m_paintLayer.containsDirtyOverlayScrollbars())
         return;
 
     PaintLayerPaintingInfo paintingInfo(&m_paintLayer, LayoutRect(enclosingIntRect(damageRect)), paintFlags, LayoutSize());
     paintLayer(context, paintingInfo, PaintLayerPaintingOverlayScrollbars);
 
     m_paintLayer.setContainsDirtyOverlayScrollbars(false);
 }
 
 } // namespace blink