Use the bounding box of all descendants for localVisualRect if there is a mask.

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>
@@ skipping 2321 matching lines @@
       if (!result.hitTestRequest().listBased())
         result = tempResult;
       if (!depthSortDescendants)
         break;
     }
   }
 
   return resultLayer;
 }
 
-FloatRect PaintLayer::boxForFilter() const {
+FloatRect PaintLayer::boxForFilterOrMask() const {
   return FloatRect(physicalBoundingBoxIncludingStackingChildren(
       LayoutPoint(), PaintLayer::CalculateBoundsOptions::
                          IncludeTransformsAndCompositedChildLayers));
 }
 
 LayoutRect PaintLayer::boxForClipPath() const {
   if (!layoutObject()->isBox()) {
     SECURITY_DCHECK(layoutObject()->isLayoutInline());
     const LayoutInline& layoutInline = toLayoutInline(*layoutObject());
     // This somewhat convoluted computation matches what Gecko does.
@@ skipping 662 matching lines @@
         BoxReflectFilterOperation::create(reflection));
   }
   return filterOperations;
 }
 
 CompositorFilterOperations
 PaintLayer::createCompositorFilterOperationsForFilter(
     const ComputedStyle& style) {
   FloatRect zoomedReferenceBox;
   if (style.filter().hasReferenceFilter())
-    zoomedReferenceBox = boxForFilter();
+    zoomedReferenceBox = boxForFilterOrMask();
   FilterEffectBuilder builder(enclosingNode(), zoomedReferenceBox,
                               style.effectiveZoom());
   return builder.buildFilterOperations(addReflectionToFilterOperations(style));
 }
 
 CompositorFilterOperations
 PaintLayer::createCompositorFilterOperationsForBackdropFilter(
     const ComputedStyle& style) {
   FloatRect zoomedReferenceBox;
   if (style.backdropFilter().hasReferenceFilter())
-    zoomedReferenceBox = boxForFilter();
+    zoomedReferenceBox = boxForFilterOrMask();
   FilterEffectBuilder builder(enclosingNode(), zoomedReferenceBox,
                               style.effectiveZoom());
   return builder.buildFilterOperations(style.backdropFilter());
 }
 
 PaintLayerResourceInfo& PaintLayer::ensureResourceInfo() {
   PaintLayerRareData& rareData = ensureRareData();
   if (!rareData.resourceInfo)
     rareData.resourceInfo = new PaintLayerResourceInfo(this);
   return *rareData.resourceInfo;
@@ skipping 27 matching lines @@
     return nullptr;
   PaintLayerResourceInfo* resourceInfo = this->resourceInfo();
   DCHECK(resourceInfo);
 
   if (resourceInfo->lastEffect())
     return resourceInfo->lastEffect();
 
   const ComputedStyle& style = layoutObject()->styleRef();
   FloatRect zoomedReferenceBox;
   if (style.filter().hasReferenceFilter())
-    zoomedReferenceBox = boxForFilter();
+    zoomedReferenceBox = boxForFilterOrMask();
   FilterEffectBuilder builder(enclosingNode(), zoomedReferenceBox,
                               style.effectiveZoom());
   resourceInfo->setLastEffect(
       builder.buildFilterEffect(addReflectionToFilterOperations(style)));
   return resourceInfo->lastEffect();
 }
 
 FloatRect PaintLayer::mapRectForFilter(const FloatRect& rect) const {
   if (!hasFilterThatMovesPixels())
     return rect;
@@ skipping 155 matching lines @@
 }
 
 void showLayerTree(const blink::LayoutObject* layoutObject) {
   if (!layoutObject) {
     LOG(INFO) << "Cannot showLayerTree. Root is (nil)";
     return;
   }
   showLayerTree(layoutObject->enclosingLayer());
 }
 #endif