[SPInvalidation] Handle pixel-snapping of paint invalidation rects

third_party/WebKit/LayoutTests/flag-specific/enable-blink-features=SlimmingPaintInvalidation/paint/invalidation/flexbox/repaint-expected.txt

 {
   "layers": [
     {
       "name": "LayoutView #document",
       "bounds": [800, 600],
       "contentsOpaque": true,
       "drawsContent": true,
       "paintInvalidations": [
         {
           "object": "LayoutBlockFlow DIV id='content'",
@@ skipping 45 matching lines @@
           "rect": [400, 128, 389, 159],
           "reason": "forced by layout"
         },
         {
           "object": "LayoutBlockFlow DIV id='left'",
           "rect": [148, 128, 252, 160],
           "reason": "incremental"
         },
         {
           "object": "LayoutBlockFlow DIV id='left'",
-          "rect": [138, 128, 10, 100],
-          "reason": "incremental"
+          "rect": [8, 128, 140, 100],
+          "reason": "bounds change"
         }
       ]
     }
   ],
   "objectPaintInvalidations": [
     {
       "object": "LayoutBlockFlow DIV id='left'",
       "reason": "incremental"
     },
     {
@@ skipping 27 matching lines @@
     {
       "object": "InlineTextBox 'tellus vel varius vestibulum, purus quam mollis sapien, in condimentum leo neque sed nulla. Nunc quis porta'",
       "reason": "forced by layout"
     },
     {
       "object": "InlineTextBox 'elit. Pellentesque erat lectus, ultricies a lobortis id, faucibus id quam.'",
       "reason": "forced by layout"
     },
     {
       "object": "LayoutBlockFlow DIV id='left'",
-      "reason": "incremental"
+      "reason": "bounds change"
     },
     {
       "object": "LayoutBlockFlow DIV id='content'",
       "reason": "style change"
     },
     {
       "object": "LayoutBlockFlow P",
       "reason": "forced by layout"
     },
     {
@@ skipping 20 matching lines @@
       "object": "InlineTextBox 'vel varius vestibulum, purus quam mollis sapien, in condimentum leo neque sed nulla. Nunc quis porta elit.'",
       "reason": "forced by layout"
     },
     {
       "object": "InlineTextBox 'Pellentesque erat lectus, ultricies a lobortis id, faucibus id quam.'",
       "reason": "forced by layout"
     }
   ]
 }