Round the subpixel accumulation used for composited scrolling content

third_party/WebKit/Source/core/frame/LocalFrame.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Simon Hausmann <hausmann@kde.org>
  *                     2000 Stefan Schimanski <1Stein@gmx.de>
  *                     2001 George Staikos <staikos@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All
  * rights reserved.
  * Copyright (C) 2005 Alexey Proskuryakov <ap@nypop.com>
@@ skipping 190 matching lines @@
     PaintLayer* layer = dragged_layout_object->EnclosingLayer();
     if (!layer->StackingNode()->IsStackingContext())
       layer = layer->StackingNode()->AncestorStackingContextNode()->Layer();
     IntRect absolute_bounding_box =
         dragged_layout_object->AbsoluteBoundingBoxRectIncludingDescendants();
     FloatRect bounding_box =
         layer->GetLayoutObject()
             .AbsoluteToLocalQuad(FloatQuad(absolute_bounding_box),
                                  kUseTransforms)
             .BoundingBox();
+    DCHECK(layer->GetCompositingState() != kPaintsIntoOwnBacking ||
+           layer->SubpixelAccumulation().IsZero());
     PaintLayerPaintingInfo painting_info(layer, LayoutRect(bounding_box),
                                          kGlobalPaintFlattenCompositingLayers,
                                          LayoutSize());
     PaintLayerFlags flags = kPaintLayerHaveTransparency |
                             kPaintLayerAppliedTransform |
                             kPaintLayerUncachedClipRects;
     PaintRecordBuilder builder(DeviceSpaceBounds(bounding_box, *local_frame_));
     PaintLayerPainter(*layer).Paint(builder.Context(), painting_info, flags);
     PropertyTreeState border_box_properties = PropertyTreeState::Root();
     if (RuntimeEnabledFeatures::slimmingPaintV2Enabled()) {
@@ skipping 725 matching lines @@
   if (frame_ && frame_->Client() && frame_->Client()->GetFrameBlameContext())
     frame_->Client()->GetFrameBlameContext()->Enter();
 }
 
 ScopedFrameBlamer::~ScopedFrameBlamer() {
   if (frame_ && frame_->Client() && frame_->Client()->GetFrameBlameContext())
     frame_->Client()->GetFrameBlameContext()->Leave();
 }
 
 }  // namespace blink