Enable slimming paint for fast/repaint

LayoutTests/fast/repaint/align-self-change-grid-expected.txt

 {
   "bounds": [800, 600],
   "children": [
     {
       "bounds": [800, 600],
       "contentsOpaque": true,
       "drawsContent": true,
       "repaintRects": [
         [100, 52, 100, 300],
         [100, 52, 100, 50],
         [0, 302, 100, 50],
         [0, 302, 100, 50],
         [0, 52, 100, 300],
         [0, 52, 100, 50]
+      ],
+      "paintInvalidationClients": [
+        "LayoutBlockFlow DIV class='item1'",
+        "LayoutBlockFlow DIV",
+        "LayoutBlockFlow DIV class='item2'"
       ]
     }
   ]
 }