Use enclosingIntRect when computing paint invalidations across transforms

third_party/WebKit/LayoutTests/paint/invalidation/invalidation-with-scale-transform-expected.txt

 {
   "name": "Content Root Layer",
   "bounds": [800, 600],
   "children": [
     {
       "name": "LayoutView #document",
       "bounds": [800, 600],
       "contentsOpaque": true,
       "drawsContent": true,
       "paintInvalidations": [
         {
           "object": "LayoutBlockFlow (positioned) DIV id='target'",
-          "rect": [20, 20, 100, 100],
+          "rect": [85, 70, 91, 92],
           "reason": "bounds change"
         },
         {
           "object": "LayoutBlockFlow (positioned) DIV id='target'",
-          "rect": [0, 0, 100, 100],
+          "rect": [84, 70, 91, 92],
           "reason": "bounds change"
         }
       ]
     }
   ],
   "objectPaintInvalidations": [
     {
       "object": "LayoutBlockFlow (positioned) DIV id='target'",
       "reason": "bounds change"
     }
   ]
 }