Move the dom directory from web-platform-tests/ to wpt/.

third_party/WebKit/LayoutTests/imported/wpt/dom/constants.js

 function testConstants(objects, constants, msg) {
   objects.forEach(function(arr) {
     var o = arr[0], desc = arr[1];
     test(function() {
       constants.forEach(function(d) {
         assert_true(d[0] in o, "Object " + o + " doesn't have " + d[0])
         assert_equals(o[d[0]], d[1], "Object " + o + " value for " + d[0] + " is wrong")
       })
     }, "Constants for " + msg + " on " + desc + ".")
   })
 }