Add a number of tests for layer squashing

LayoutTests/compositing/squashing/squash-simple-expected.txt

Index: LayoutTests/compositing/squashing/squash-simple-expected.txt
diff --git a/LayoutTests/compositing/contents-opaque/body-background-skipped-expected.txt b/LayoutTests/compositing/squashing/squash-simple-expected.txt
similarity index 64%
copy from LayoutTests/compositing/contents-opaque/body-background-skipped-expected.txt
copy to LayoutTests/compositing/squashing/squash-simple-expected.txt
index cd1c4d7a31db633e404586c52180bb48fbd0eba6..c5662d446ff3708192d097135ae25cee1164e996 100644
--- a/LayoutTests/compositing/contents-opaque/body-background-skipped-expected.txt
+++ b/LayoutTests/compositing/squashing/squash-simple-expected.txt
@@ -4,19 +4,18 @@
     (GraphicsLayer
       (bounds 800.00 600.00)
       (contentsOpaque 1)
+      (drawsContent 1)
       (children 1
         (GraphicsLayer
-          (bounds 800.00 600.00)
-          (drawsContent 1)
-          (backgroundColor #0000FF)
           (children 2
             (GraphicsLayer
-              (position 8.00 8.00)
-              (bounds 200.00 200.00)
+              (position 100.00 100.00)
+              (bounds 100.00 100.00)
               (contentsOpaque 1)
             )
             (GraphicsLayer
-              (bounds 800.00 600.00)
+              (position 20.00 20.00)
+              (bounds 260.00 260.00)
               (drawsContent 1)
             )
           )