Simplify application of perspective origin.

LayoutTests/platform/win/compositing/overflow/reparented-overlay-scrollbars-with-non-stacking-context-compositing-ancestor-expected.txt

 {
   "bounds": [1208, 821],
   "children": [
     {
       "bounds": [1208, 821],
       "contentsOpaque": true,
       "drawsContent": true,
       "children": [
         {
           "position": [8, 8],
@@ skipping 13 matching lines @@
                       "children": [
                         {
                           "bounds": [1200, 1000],
                           "drawsContent": true,
                           "children": [
                             {
                               "bounds": [1200, 1000],
                               "children": [
                                 {
                                   "bounds": [1200, 10000],
-                                  "shouldFlattenTransform": false,
                                   "drawsContent": true,
                                   "children": [
                                     {
-                                      "shouldFlattenTransform": false
+
                                     }
                                   ]
                                 }
                               ]
                             }
                           ]
                         }
                       ]
                     }
                   ]
@@ skipping 19 matching lines @@
                 }
               ]
             }
           ]
         }
       ]
     }
   ]
 }