Fix paint invalidation when composited layers change from paints-into-ancestor to self-painting.

LayoutTests/compositing/change-from-paints-into-ancestor-to-paints-into-own-backing-for-intrinsic-reason-expected.txt

 {
   "bounds": [800, 600],
   "children": [
     {
       "bounds": [800, 600],
       "contentsOpaque": true,
       "drawsContent": true,
+      "repaintRects": [
+        [8, 8, 784, 100]
+      ],
       "children": [
         {
           "position": [8, 8],
+          "bounds": [784, 100],
+          "opacity": 0,
+          "contentsOpaque": true,
+          "drawsContent": true,
+          "backgroundColor": "#FF0000",
+          "repaintRects": [
+            [0, 0, 784, 100],
+            [0, 0, 784, 100]
+          ],
           "children": [
             {
+              "bounds": [784, 100],
               "shouldFlattenTransform": false,
               "transform": [
                 [1, 0, 0, 0],
                 [0, 1, 0, 0],
-                [0, 0, 1, -0.001],
+                [0, 0, 1, -1],
                 [0, 0, 0, 1]
               ],
               "children": [
                 {
-                  "bounds": [200, 200],
+                  "bounds": [100, 100],
                   "contentsOpaque": true,
                   "drawsContent": true,
-                  "backgroundColor": "#00008B",
-                  "transform": [
-                    [1, 0, 0, 0],
-                    [0, 1, 0, 0],
-                    [0, 0, 1, 0],
-                    [0, 74, 200, 1]
-                  ]
+                  "backfaceVisibility": "hidden",
+                  "backgroundColor": "#0000FF"
                 }
               ]
             }
           ]
-        },
-        {
-          "position": [8, 8]
         }
       ]
     }
   ]
 }