Add a number of tests for layer squashing

LayoutTests/compositing/squashing/squash-onto-nephew-expected.txt

Index: LayoutTests/compositing/squashing/squash-onto-nephew-expected.txt
diff --git a/LayoutTests/compositing/squashing/squash-onto-nephew-expected.txt b/LayoutTests/compositing/squashing/squash-onto-nephew-expected.txt
new file mode 100644
index 0000000000000000000000000000000000000000..809ba0213f931ef17cf04ad088b9c8e2da7e3968
--- /dev/null
+++ b/LayoutTests/compositing/squashing/squash-onto-nephew-expected.txt
@@ -0,0 +1,39 @@
+(GraphicsLayer
+  (bounds 800.00 600.00)
+  (children 1
+    (GraphicsLayer
+      (bounds 800.00 600.00)
+      (contentsOpaque 1)
+      (drawsContent 1)
+      (children 1
+        (GraphicsLayer
+          (position 25.00 25.00)
+          (bounds 300.00 300.00)
+          (contentsOpaque 1)
+          (backgroundColor #808080)
+          (children 1
+            (GraphicsLayer
+              (bounds 300.00 300.00)
+              (children 1
+                (GraphicsLayer
+                  (children 2
+                    (GraphicsLayer
+                      (position 100.00 100.00)
+                      (bounds 100.00 100.00)
+                      (contentsOpaque 1)
+                    )
+                    (GraphicsLayer
+                      (bounds 300.00 300.00)
+                      (drawsContent 1)
+                    )
+                  )
+                )
+              )
+            )
+          )
+        )
+      )
+    )
+  )
+)
+