Add a UseCounter for clip CSS or -webkit-clip-path that clips positioned descendants.

Source/core/paint/DeprecatedPaintLayerPaintingInfo.h

Index: Source/core/paint/DeprecatedPaintLayerPaintingInfo.h
diff --git a/Source/core/paint/DeprecatedPaintLayerPaintingInfo.h b/Source/core/paint/DeprecatedPaintLayerPaintingInfo.h
index 52889798992189806ec2ace2990c96f8ca9d04c9..dc217b40b311c5af2f4f80656d021c629ae0b7f3 100644
--- a/Source/core/paint/DeprecatedPaintLayerPaintingInfo.h
+++ b/Source/core/paint/DeprecatedPaintLayerPaintingInfo.h
@@ -85,6 +85,7 @@ struct DeprecatedPaintLayerPaintingInfo {
         , paintDirtyRect(inDirtyRect)
         , subPixelAccumulation(inSubPixelAccumulation)
         , clipToDirtyRect(true)
+        , ancestorHasClipPathClipping(false)
         , m_globalPaintFlags(globalPaintFlags)
     { }
 
@@ -97,6 +98,7 @@ struct DeprecatedPaintLayerPaintingInfo {
     LayoutSize subPixelAccumulation;
     IntSize scrollOffsetAccumulation;
     bool clipToDirtyRect;
+    bool ancestorHasClipPathClipping;
 
 private:
     const GlobalPaintFlags m_globalPaintFlags;