Use unfragmented clip bounds when fragmentation is inhibited due to compositing

third_party/WebKit/Source/core/paint/PaintLayer.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 1115 matching lines @@
         // get our true bounding box.
         LayoutFlowThread* enclosingFlowThread = toLayoutFlowThread(paginationLayer->layoutObject());
         result = enclosingFlowThread->fragmentsBoundingBox(result);
 
         LayoutPoint rootLayerDelta;
         paginationLayer->convertToLayerCoords(rootLayer, rootLayerDelta);
         result.moveBy(rootLayerDelta);
         return result;
     }
 
-    LayoutRect clipRect = layer->fragmentsBoundingBox(rootLayer);
+    LayoutRect clipRect = layer->shouldFragmentCompositedBounds(rootLayer) ? layer->fragmentsBoundingBox(rootLayer) : layer->physicalBoundingBox(rootLayer);
     expandClipRectForDescendantsAndReflection(clipRect, layer, rootLayer, transparencyBehavior, subPixelAccumulation, globalPaintFlags);
     clipRect = layer->mapLayoutRectForFilter(clipRect);
     clipRect.move(subPixelAccumulation);
     return clipRect;
 }
 
 LayoutRect PaintLayer::paintingExtent(const PaintLayer* rootLayer, const LayoutSize& subPixelAccumulation, GlobalPaintFlags globalPaintFlags)
 {
     return transparencyClipBox(this, rootLayer, PaintingTransparencyClipBox, RootOfTransparencyClipBox, subPixelAccumulation, globalPaintFlags);
 }
@@ skipping 1010 matching lines @@
 
     LayoutRect result = flippedLogicalBoundingBox(logicalBoundingBox(), layoutObject());
     convertFromFlowThreadToVisualBoundingBoxInAncestor(ancestorLayer, result);
     return result;
 }
 
 LayoutRect PaintLayer::boundingBoxForCompositingOverlapTest() const
 {
     // Apply NeverIncludeTransformForAncestorLayer, because the geometry map in CompositingInputsUpdater will take care of applying the
     // transform of |this| (== the ancestorLayer argument to boundingBoxForCompositing).
+    // TODO(trchen): Layer fragmentation is inhibited across compositing boundary. Should we
+    // return the unfragmented bounds for overlap testing? Or perhaps assume fragmented layers
+    // always overlap?
     return overlapBoundsIncludeChildren() ? boundingBoxForCompositing(this, NeverIncludeTransformForAncestorLayer) : fragmentsBoundingBox(this);
 }
 
 bool PaintLayer::overlapBoundsIncludeChildren() const
 {
     const auto* style = layoutObject()->style();
     if (style && style->filter().hasFilterThatMovesPixels())
         return true;
     if (RuntimeEnabledFeatures::cssBoxReflectFilterEnabled() && layoutObject()->hasReflection())
         return true;
@@ skipping 766 matching lines @@
 
 void showLayerTree(const blink::LayoutObject* layoutObject)
 {
     if (!layoutObject) {
         fprintf(stderr, "Cannot showLayerTree. Root is (nil)\n");
         return;
     }
     showLayerTree(layoutObject->enclosingLayer());
 }
 #endif