Fix pixel snapping of stacked sub-pixel composited layers

LayoutTests/compositing/repaint/should-not-repaint-composited-styles-expected.txt

 position change with composited child
 
 position change with non-composited child
 
 z-index change with composited child
 
 z-index change with non-composited child
 
 opacity change with composited child
 
@@ skipping 17 matching lines @@
       (children 10
         (GraphicsLayer
           (position 8.00 80.00)
           (bounds 100.00 100.00)
           (children 1
             (GraphicsLayer
               (position 0.00 -1.00)
               (bounds 100.00 100.00)
               (children 1
                 (GraphicsLayer
+                  (position 0.00 1.00)
                   (bounds 152.00 152.00)
                   (contentsOpaque 1)
                   (drawsContent 1)
                   (backgroundColor #FFFF00)
                 )
               )
             )
           )
         )
         (GraphicsLayer
@@ skipping 64 matching lines @@
           (drawsContent 1)
           (repaint rects
             (rect 0.00 0.00 100.00 100.00)
           )
           (children 1
             (GraphicsLayer
               (position 0.00 -1.00)
               (bounds 100.00 100.00)
               (children 1
                 (GraphicsLayer
+                  (position 0.00 1.00)
                   (bounds 152.00 152.00)
                   (contentsOpaque 1)
                   (drawsContent 1)
                   (backgroundColor #FFFF00)
                 )
               )
             )
           )
         )
         (GraphicsLayer
           (position 8.00 1699.00)
           (bounds 100.00 100.00)
           (drawsContent 1)
           (repaint rects
             (rect 0.00 0.00 100.00 100.00)
           )
         )
         (GraphicsLayer
           (position 8.00 440.00)
           (bounds 100.00 100.00)
           (children 1
             (GraphicsLayer
               (position 0.00 -1.00)
               (bounds 100.00 100.00)
               (children 1
                 (GraphicsLayer
+                  (position 0.00 1.00)
                   (bounds 152.00 152.00)
                   (contentsOpaque 1)
                   (drawsContent 1)
                   (backgroundColor #FFFF00)
                 )
               )
             )
           )
         )
         (GraphicsLayer
           (position 8.00 620.00)
           (bounds 100.00 100.00)
           (drawsContent 1)
           (repaint rects
             (rect 0.00 0.00 100.00 100.00)
           )
         )
       )
     )
   )
 )