[SPInvalidation] Handle pixel-snapping of paint invalidation rects

third_party/WebKit/LayoutTests/flag-specific/enable-blink-features=SlimmingPaintInvalidation/paint/invalidation/line-flow-with-floats-4-expected.txt

 {
   "layers": [
     {
       "name": "LayoutView #document",
       "bounds": [800, 600],
       "contentsOpaque": true,
       "drawsContent": true,
       "paintInvalidations": [
         {
           "object": "LayoutText #text",
@@ skipping 25 matching lines @@
           "rect": [134, 360, 131, 19],
           "reason": "forced by layout"
         },
         {
           "object": "LayoutText #text",
           "rect": [303, 420, 66, 19],
           "reason": "forced by layout"
         },
         {
           "object": "LayoutBlockFlow (floating) SPAN id='greenFloat'",
-          "rect": [372, 447, 48, 17],
-          "reason": "incremental"
+          "rect": [372, 383, 48, 81],
+          "reason": "bounds change"
         }
       ]
     }
   ],
   "objectPaintInvalidations": [
     {
       "object": "LayoutText #text",
       "reason": "forced by layout"
     },
     {
@@ skipping 55 matching lines @@
     {
       "object": "LayoutText #text",
       "reason": "forced by layout"
     },
     {
       "object": "InlineTextBox 'The players all played at once without waiting\n'",
       "reason": "forced by layout"
     },
     {
       "object": "LayoutBlockFlow (floating) SPAN id='greenFloat'",
-      "reason": "incremental"
+      "reason": "bounds change"
     },
     {
       "object": "LayoutText #text",
       "reason": "forced by layout"
     },
     {
       "object": "InlineTextBox 'for'",
       "reason": "forced by layout"
     },
     {
@@ skipping 76 matching lines @@
       "object": "InlineTextBox 'They\u2019re dreadfully fond of beheading people here; the great'",
       "reason": "forced by layout"
     },
     {
       "object": "InlineTextBox 'wonder is, that there\u2018s any one left alive!\u2019'",
       "reason": "forced by layout"
     }
   ]
 }