Enable slimming paint for fast/repaint

LayoutTests/platform/mac/fast/repaint/line-flow-with-floats-4-expected.txt

 {
   "bounds": [800, 600],
   "children": [
     {
       "bounds": [800, 600],
       "contentsOpaque": true,
       "drawsContent": true,
       "repaintRects": [
         [372, 435, 48, 16],
         [369, 422, 52, 54],
         [8, 368, 418, 108]
+      ],
+      "paintInvalidationClients": [
+        "InlineTextBox 'The players all played at once without waiting'",
+        "RootInlineBox",
+        "InlineTextBox 'for turns,\n'",
+        "InlineTextBox 'quarrelling all the while, and fighting'",
+        "RootInlineBox",
+        "InlineTextBox 'for the hedgehogs; and in\n'",
+        "InlineTextBox 'a very short time '",
+        "InlineTextBox 'the'",
+        "RootInlineBox",
+        "InlineTextBox 'Queen'",
+        "InlineTextBox ' was in a furious passion, and went\n'",
+        "InlineTextBox 'stamping'",
+        "RootInlineBox",
+        "InlineTextBox 'about, and shouting \u2018Off with his head!\u2019 or \u2018Off with'",
+        "RootInlineBox",
+        "InlineTextBox 'her head!\u2019 about once in a minute.\n'",
+        "RootInlineBox",
+        "LayoutBlockFlow P",
+        "LayoutBlockFlow (floating) SPAN id='greenFloat'",
+        "LayoutText #text",
+        "InlineTextBox ' was in a furious passion, and went\n'",
+        "InlineTextBox 'stamping'",
+        "InlineTextBox 'about, and shouting \u2018Off with his head!\u2019 or \u2018Off with\n'",
+        "InlineTextBox 'her'",
+        "InlineTextBox 'head!\u2019 about once in a minute.\n'"
       ]
     }
   ]
 }