Fix unittests

LayoutTests/platform/mac/virtual/software/compositing/tiling/huge-layer-with-layer-children-expected.txt

 The yellow box should be large enough to scroll off the bottom. There should be a red box on the first page and a blue box near the bottom of the yellow box. This tests that we can support very large compositing layers with child compositing layers.
 
 This is some text
 (GraphicsLayer
   (bounds 785.00 5129.00)
   (children 1
     (GraphicsLayer
       (bounds 785.00 5129.00)
       (contentsOpaque 1)
       (drawsContent 1)
@@ skipping 19 matching lines @@
               (drawsContent 1)
               (backgroundColor #0000FF)
             )
           )
         )
       )
     )
   )
 )