Implement -webkit-box-reflect as a filter.

third_party/WebKit/Source/core/layout/LayoutObject.h

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  *           (C) 2000 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 700 matching lines @@
 
     bool hasClip() const { return isOutOfFlowPositioned() && !style()->hasAutoClip(); }
     bool hasOverflowClip() const { return m_bitfields.hasOverflowClip(); }
     bool hasClipRelatedProperty() const { return hasClip() || hasOverflowClip() || style()->containsPaint(); }
 
     bool hasTransformRelatedProperty() const { return m_bitfields.hasTransformRelatedProperty(); }
     bool hasMask() const { return style() && style()->hasMask(); }
     bool hasClipPath() const { return style() && style()->clipPath(); }
     bool hasHiddenBackface() const { return style() && style()->backfaceVisibility() == BackfaceVisibilityHidden; }
 
     bool hasFilter() const { return style() && style()->hasFilter(); }

[pdr., 2016/03/29 18:36:55]

Would it be cleaner to update paintInvalidationState::supportsCachedOffsets to
call "hasFilterInducingProperty" too?

With that change, I think we can remove hasFilter entirely. I think this will
keep us from making mistakes in the future.

     bool hasBackdropFilter() const { return style() && style()->hasBackdropFilter(); }
+    bool hasFilterInducingProperty() const

[Stephen White, 2016/03/30 14:41:35]

I find this name unintuitive. Could we be more explicit, e.g.,
hasFilterOrReflection()?

Think about it from the point-of-view of someone new to this code: what is a
filter-inducing property? Is this a fundamental property or an implementation
detail? You could explain it with a comment, but Blink style is to put it in the
name.

+    {
+        return (style() && style()->hasFilter()) || (RuntimeEnabledFeatures::cssBoxReflectFilterEnabled() && hasReflection());
+    }
 
     bool hasShapeOutside() const { return style() && style()->shapeOutside(); }
 
     inline bool preservesNewline() const;
 
     // The pseudo element style can be cached or uncached.  Use the cached method if the pseudo element doesn't respect
     // any pseudo classes (and therefore has no concept of changing state).
     ComputedStyle* getCachedPseudoStyle(PseudoId, const ComputedStyle* parentStyle = nullptr) const;
     PassRefPtr<ComputedStyle> getUncachedPseudoStyle(const PseudoStyleRequest&, const ComputedStyle* parentStyle = nullptr, const ComputedStyle* ownStyle = nullptr) const;
 
@@ skipping 524 matching lines @@
         return mapAncestorToLocal(nullptr, transformState, flags);
     }
 
     // Pushes state onto LayoutGeometryMap about how to map coordinates from this layoutObject to its container, or ancestorToStopAt (whichever is encountered first).
     // Returns the layoutObject which was mapped to (container or ancestorToStopAt).
     virtual const LayoutObject* pushMappingToContainer(const LayoutBoxModelObject* ancestorToStopAt, LayoutGeometryMap&) const;
 
     bool shouldUseTransformFromContainer(const LayoutObject* container) const;
     void getTransformFromContainer(const LayoutObject* container, const LayoutSize& offsetInContainer, TransformationMatrix&) const;
 
-    bool createsGroup() const { return isTransparent() || hasMask() || hasFilter() || style()->hasBlendMode(); }
+    bool createsGroup() const { return isTransparent() || hasMask() || hasFilterInducingProperty() || style()->hasBlendMode(); }
 
     // Collects rectangles that the outline of this object would be drawing along the outside of,
     // even if the object isn't styled with a outline for now. The rects also cover continuations.
     enum IncludeBlockVisualOverflowOrNot {
         DontIncludeBlockVisualOverflow,
         IncludeBlockVisualOverflow,
     };
     virtual void addOutlineRects(Vector<LayoutRect>&, const LayoutPoint& additionalOffset, IncludeBlockVisualOverflowOrNot) const { }
 
     // For history and compatibility reasons, we draw outline:auto (for focus rings) and normal style outline differently.
@@ skipping 886 matching lines @@
 void showTree(const blink::LayoutObject*);
 void showLineTree(const blink::LayoutObject*);
 void showLayoutTree(const blink::LayoutObject* object1);
 // We don't make object2 an optional parameter so that showLayoutTree
 // can be called from gdb easily.
 void showLayoutTree(const blink::LayoutObject* object1, const blink::LayoutObject* object2);
 
 #endif
 
 #endif // LayoutObject_h