Re-attach plugin renderers in the standard way.

LayoutTests/svg/as-object/embedded-svg-size-changes-no-layout-triggers-expected.txt

 {
   "bounds": [800, 600],
   "children": [
     {
       "bounds": [800, 600],
       "contentsOpaque": true,
       "drawsContent": true,
       "repaintRects": [
         [286, 1, 15, 150],
         [286, 1, 15, 150],
         [1, 1, 300, 150],
         [1, 1, 15, 15],
-        [0, 0, 800, 152],
+        [0, 0, 800, 600],
         [0, 0, 302, 152],
         [0, 0, 300, 150]
       ]
     }
   ]
 }