[Blink>Paint] Document element cannot always omit isolation

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/LocalFrame.h"
 #include "core/layout/LayoutView.h"
 #include "core/paint/ClipPathClipper.h"
 #include "core/paint/FilterPainter.h"
@@ skipping 372 matching lines @@
           paintingInfo.rootLayer, referenceBox);
     else
       referenceBox.moveBy(offsetFromRoot);
     clipPathClipper.emplace(
         context, *m_paintLayer.layoutObject()->styleRef().clipPath(),
         *m_paintLayer.layoutObject(), FloatRect(referenceBox),
         FloatPoint(referenceBox.location()));
   }
 
   Optional<CompositingRecorder> compositingRecorder;
-  // Blending operations must be performed only with the nearest ancestor
-  // stacking context.  Note that there is no need to composite if we're
-  // painting the root.
   // FIXME: this should be unified further into
   // PaintLayer::paintsWithTransparency().
   bool shouldCompositeForBlendMode =
-      (!m_paintLayer.layoutObject()->isDocumentElement() ||
-       m_paintLayer.layoutObject()->isSVGRoot()) &&
       m_paintLayer.stackingNode()->isStackingContext() &&
       m_paintLayer.hasNonIsolatedDescendantWithBlendMode();
   if (shouldCompositeForBlendMode ||
       m_paintLayer.paintsWithTransparency(paintingInfo.getGlobalPaintFlags())) {
     FloatRect compositingBounds = FloatRect(m_paintLayer.paintingExtent(
         paintingInfo.rootLayer, paintingInfo.subPixelAccumulation,
         paintingInfo.getGlobalPaintFlags()));
     compositingRecorder.emplace(
         context, *m_paintLayer.layoutObject(),
         WebCoreCompositeToSkiaComposite(
@@ skipping 712 matching lines @@
 
   PaintLayerPaintingInfo paintingInfo(&m_paintLayer,
                                       LayoutRect(enclosingIntRect(damageRect)),
                                       paintFlags, LayoutSize());
   paintLayer(context, paintingInfo, PaintLayerPaintingOverlayScrollbars);
 
   m_paintLayer.setContainsDirtyOverlayScrollbars(false);
 }
 
 }  // namespace blink