Fixing 2D canvas invalidation region tracking.

LayoutTests/compositing/layer-creation/should-invoke-deferred-compositing-expected.txt

 {
   "bounds": [800, 600],
   "children": [
     {
       "bounds": [800, 600],
       "contentsOpaque": true,
       "drawsContent": true,
       "children": [
         {
           "bounds": [300, 300],
           "children": [
             {
-              "bounds": [200, 200]
+              "bounds": [200, 200],
+              "drawsContent": true,
+              "repaintRects": [
+                [0, 0, 200, 200],
+                [0, 0, 200, 200]
+              ]
             }
           ]
         }
       ]
     }
   ]
 }