Fix squashing to treat perspective and preserve3d elements as transform ancestors.

LayoutTests/compositing/squashing/squashing-inside-perspective-expected.txt

 {
   "bounds": [800, 600],
   "children": [
     {
       "bounds": [800, 600],
       "contentsOpaque": true,
       "drawsContent": true,
       "children": [
         {
           "position": [8, 8],
-          "bounds": [122, 242],
           "children": [
             {
-              "position": [1, 1],
-              "bounds": [120, 240],
+              "shouldFlattenTransform": false,
+              "transform": [
+                [1, 0, 0, 0],
+                [0, 1, 0, 0],
+                [0, 0, 1, -0.001],
+                [0, 0, 0, 1]
+              ],
               "children": [
                 {
-                  "position": [10, 10],
-                  "bounds": [100, 100],
+                  "bounds": [200, 200],
                   "contentsOpaque": true,
                   "drawsContent": true,
-                  "backgroundColor": "#0000FF",
+                  "backgroundColor": "#00008B",
                   "transform": [
                     [1, 0, 0, 0],
                     [0, 1, 0, 0],
                     [0, 0, 1, 0],
-                    [0, 0, 1, 1]
+                    [0, 74, 200, 1]
                   ]
                 }
               ]
             }
           ]
+        },
+        {
+          "position": [8, 8]
         }
       ]
     }
   ]
 }