Disable solid background color optimization for composited layers.

LayoutTests/compositing/geometry/limit-layer-bounds-transformed-expected.txt

 Text here
 (GraphicsLayer
   (bounds 800.00 600.00)
   (children 1
     (GraphicsLayer
       (bounds 800.00 600.00)
       (contentsOpaque 1)
       (children 3
         (GraphicsLayer
           (position 129.00 29.00)
           (bounds 100.00 100.00)
         )
         (GraphicsLayer
           (position 129.00 29.00)
           (bounds 200.00 100.00)
           (contentsOpaque 1)
+          (drawsContent 1)
+          (backgroundColor #FF0000)
         )
         (GraphicsLayer
           (position -971.00 8.00)
           (anchor 0.90 0.50)
           (bounds 1221.00 142.00)
           (drawsContent 1)
           (transform [1.00 0.00 0.00 0.00] [0.00 1.00 0.00 0.00] [0.00 0.00 1.00 0.00] [100.00 0.00 0.00 1.00])
         )
       )
     )
   )
 )