Paint carets at pixel-snapped positions.

third_party/WebKit/LayoutTests/paint/caret/caret-subpixel-expected.txt

 {
   "name": "Content Root Layer",
   "bounds": [800, 600],
   "children": [
     {
       "name": "LayoutView #document",
       "bounds": [800, 600],
       "contentsOpaque": true,
       "drawsContent": true,
       "paintInvalidations": [
         {
-          "object": "LayoutTextControl TEXTAREA",
-          "rect": [8, 8, 106, 106],
+          "object": "LayoutTextControl INPUT id='target'",
+          "rect": [8, 8, 224, 22],
           "reason": "subtree"
         },
         {
           "object": "LayoutBlockFlow DIV id='inner-editor'",
-          "rect": [11, 11, 100, 10],
+          "rect": [10, 11, 201, 16],
           "reason": "subtree"
+        },
+        {
+          "object": "LayoutBlockFlow DIV id='inner-editor'",
+          "rect": [208, 10, 4, 18],
+          "reason": "invalidate paint rectangle"
         }
       ]
     }
   ],
   "objectPaintInvalidations": [
     {
-      "object": "LayoutTextControl TEXTAREA",
+      "object": "LayoutTextControl INPUT id='target'",
       "reason": "subtree"
     },
     {
       "object": "LayoutBlockFlow DIV id='inner-editor'",
       "reason": "subtree"
+    },
+    {
+      "object": "Caret",
+      "reason": "invalidate paint rectangle"
     }
   ]
 }