Implement -webkit-box-reflect as a filter.

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

Index: third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp b/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
index 000a0c285e4211aa0adab7f7db558ebcdc01e0cc..50cf8909f8d7707404891c2771710465986c82a3 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
@@ -108,7 +108,7 @@ PaintLayerPainter::PaintResult PaintLayerPainter::paintLayerContentsAndReflectio
     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;