Fix pixel snapping of clipLayers and their descendants

Source/core/rendering/compositing/CompositedLayerMapping.cpp

Index: Source/core/rendering/compositing/CompositedLayerMapping.cpp
diff --git a/Source/core/rendering/compositing/CompositedLayerMapping.cpp b/Source/core/rendering/compositing/CompositedLayerMapping.cpp
index 03e8253d53911833144dec3b9def328aa86aad36..84db383411f7e43dd610aada822077f9fd2a7946 100644
--- a/Source/core/rendering/compositing/CompositedLayerMapping.cpp
+++ b/Source/core/rendering/compositing/CompositedLayerMapping.cpp
@@ -696,7 +696,7 @@ GraphicsLayerUpdater::UpdateType CompositedLayerMapping::updateGraphicsLayerGeom
         // If the compositing ancestor has a layer to clip children, we parent in that, and therefore
         // position relative to it.
         IntRect clippingBox = clipBox(toRenderBox(compAncestor->renderer()));
-        graphicsLayerParentLocation = clippingBox.location();
+        graphicsLayerParentLocation = clippingBox.location() + roundedIntSize(compAncestor->compositedLayerMapping()->subpixelAccumulation());
     } else if (compAncestor) {
         graphicsLayerParentLocation = ancestorCompositingBounds.location();
     } else {
@@ -737,7 +737,7 @@ GraphicsLayerUpdater::UpdateType CompositedLayerMapping::updateGraphicsLayerGeom
     IntRect clippingBox;
     if (GraphicsLayer* clipLayer = clippingLayer()) {
         clippingBox = clipBox(toRenderBox(renderer()));
-        clipLayer->setPosition(FloatPoint(clippingBox.location() - localCompositingBounds.location()));
+        clipLayer->setPosition(FloatPoint(clippingBox.location() - localCompositingBounds.location() + roundedIntSize(m_subpixelAccumulation)));
         clipLayer->setSize(clippingBox.size());
         clipLayer->setOffsetFromRenderer(toIntSize(clippingBox.location()));
         if (m_childClippingMaskLayer && !m_scrollingLayer) {