Don't always repaint on zIndex change

Source/core/rendering/style/RenderStyleConstants.h

Index: Source/core/rendering/style/RenderStyleConstants.h
diff --git a/Source/core/rendering/style/RenderStyleConstants.h b/Source/core/rendering/style/RenderStyleConstants.h
index 571904b36beb219f4056cd704226800145b2c578..a3afa7b0218cca2d653235ed9966db1908445092 100644
--- a/Source/core/rendering/style/RenderStyleConstants.h
+++ b/Source/core/rendering/style/RenderStyleConstants.h
@@ -75,9 +75,10 @@ enum StyleDifferenceContextSensitiveProperty {
     ContextSensitivePropertyNone = 0,
     ContextSensitivePropertyTransform = (1 << 0),
     ContextSensitivePropertyOpacity = (1 << 1),
-    ContextSensitivePropertyFilter = (1 << 2),
+    ContextSensitivePropertyZIndex = (1 << 2),
+    ContextSensitivePropertyFilter = (1 << 3),
     // The object needs to be repainted if it contains text or properties dependent on color (e.g., border or outline).
-    ContextSensitivePropertyTextOrColor = (1 << 3)
+    ContextSensitivePropertyTextOrColor = (1 << 4)
 };
 
 // Static pseudo styles. Dynamic ones are produced on the fly.