Implement -webkit-box-reflect as a filter.

third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/paint/PaintLayerPainter.h"
 
 #include "core/frame/FrameView.h"
 #include "core/frame/Settings.h"
 #include "core/layout/ClipPathOperation.h"
 #include "core/layout/LayoutBlock.h"
@@ skipping 90 matching lines @@
 
 PaintLayerPainter::PaintResult PaintLayerPainter::paintLayerContentsAndReflection(GraphicsContext& context, const PaintLayerPaintingInfo& paintingInfo, PaintLayerFlags paintFlags, FragmentPolicy fragmentPolicy)
 {
     ASSERT(m_paintLayer.isSelfPaintingLayer() || m_paintLayer.hasSelfPaintingLayerDescendant());
 
     PaintLayerFlags localPaintFlags = paintFlags & ~(PaintLayerAppliedTransform);
 
     PaintResult result = FullyPainted;
 
     // Paint the reflection first if we have one.
-    if (m_paintLayer.reflectionInfo()) {
+    if (m_paintLayer.reflectionInfo() && !RuntimeEnabledFeatures::cssBoxReflectFilterEnabled()) {

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

It seems fragile to have to check this flag in so many places. Would it be
possible to check the runtime flag once, and prevent reflectionInfo() or
hasReflection() being set in the first place?

         ScopeRecorder scopeRecorder(context);
         if (m_paintLayer.reflectionInfo()->paint(context, paintingInfo, localPaintFlags) == MayBeClippedByPaintDirtyRect)
             result = MayBeClippedByPaintDirtyRect;
     }
 
     localPaintFlags |= PaintLayerPaintingCompositingAllPhases;
     if (paintLayerContents(context, paintingInfo, localPaintFlags, fragmentPolicy) == MayBeClippedByPaintDirtyRect)
         result = MayBeClippedByPaintDirtyRect;
 
     return result;
@@ skipping 652 matching lines @@
     if (!m_paintLayer.containsDirtyOverlayScrollbars())
         return;
 
     PaintLayerPaintingInfo paintingInfo(&m_paintLayer, LayoutRect(enclosingIntRect(damageRect)), paintFlags, LayoutSize());
     paintLayer(context, paintingInfo, PaintLayerPaintingOverlayScrollbars);
 
     m_paintLayer.setContainsDirtyOverlayScrollbars(false);
 }
 
 } // namespace blink