[Reland] Correct fixed-position recording for Slimming Paint

Source/core/paint/DeprecatedPaintLayer.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 1148 matching lines @@
         // the transformed layer and all of its children.
         const DeprecatedPaintLayer* paginationLayer = transparencyMode == DescendantsOfTransparencyClipBox ? layer->enclosingPaginationLayer() : 0;
         const DeprecatedPaintLayer* rootLayerForTransform = paginationLayer ? paginationLayer : rootLayer;
         LayoutPoint delta;
         layer->convertToLayerCoords(rootLayerForTransform, delta);
 
         delta.move(subPixelAccumulation);
         IntPoint pixelSnappedDelta = roundedIntPoint(delta);
         TransformationMatrix transform;
         transform.translate(pixelSnappedDelta.x(), pixelSnappedDelta.y());
-        transform = transform * *layer->transform();
+        if (layer->transform())
+            transform = transform * *layer->transform();
 
         // We don't use fragment boxes when collecting a transformed layer's bounding box, since it always
         // paints unfragmented.
         LayoutRect clipRect = layer->physicalBoundingBox(layer);
         expandClipRectForDescendantsAndReflection(clipRect, layer, layer, transparencyBehavior, subPixelAccumulation, paintBehavior);
         clipRect.expand(layer->layoutObject()->style()->filterOutsets());
         LayoutRect result = transform.mapRect(clipRect);
         if (!paginationLayer)
             return result;
 
@@ skipping 1301 matching lines @@
             expandRectForReflectionAndStackingChildren(parent(), options, result);
         else
             expandRectForReflectionAndStackingChildren(this, options, result);
 
         // FIXME: We can optimize the size of the composited layers, by not enlarging
         // filtered areas with the outsets if we know that the filter is going to render in hardware.
         // https://bugs.webkit.org/show_bug.cgi?id=81239
         result.expand(m_layoutObject->style()->filterOutsets());
     }
 
-    if (paintsWithTransform(PaintBehaviorNormal) || (options == ApplyBoundsChickenEggHacks && transform()))
+    if (transform() && (paintsWithTransform(PaintBehaviorNormal) || options == ApplyBoundsChickenEggHacks))
         result = transform()->mapRect(result);
 
     if (enclosingPaginationLayer()) {
         convertFromFlowThreadToVisualBoundingBoxInAncestor(this, ancestorLayer, result);
         return result;
     }
     LayoutPoint delta;
     convertToLayerCoords(ancestorLayer, delta);
     result.moveBy(delta);
     return result;
@@ skipping 101 matching lines @@
     return m_compositedDeprecatedPaintLayerMapping && m_compositedDeprecatedPaintLayerMapping->hasMaskLayer();
 }
 
 bool DeprecatedPaintLayer::hasCompositedClippingMask() const
 {
     return m_compositedDeprecatedPaintLayerMapping && m_compositedDeprecatedPaintLayerMapping->hasChildClippingMaskLayer();
 }
 
 bool DeprecatedPaintLayer::paintsWithTransform(PaintBehavior paintBehavior) const
 {
-    return transform() && ((paintBehavior & PaintBehaviorFlattenCompositingLayers) || compositingState() != PaintsIntoOwnBacking);
+    return (transform() || layoutObject()->style()->position() == FixedPosition) && ((paintBehavior & PaintBehaviorFlattenCompositingLayers) || compositingState() != PaintsIntoOwnBacking);
 }
 
 bool DeprecatedPaintLayer::backgroundIsKnownToBeOpaqueInRect(const LayoutRect& localRect) const
 {
     if (!isSelfPaintingLayer() && !hasSelfPaintingLayerDescendant())
         return false;
 
     if (paintsWithTransparency(PaintBehaviorNormal))
         return false;
 
@@ skipping 353 matching lines @@
     }
 }
 
 void showLayerTree(const blink::LayoutObject* layoutObject)
 {
     if (!layoutObject)
         return;
     showLayerTree(layoutObject->enclosingLayer());
 }
 #endif