dart2js dart:html conversions for serialized script values.

tests/html/utils.dart

 #library('TestUtils');
 
 /**
  * Verifies that [actual] has the same graph structure as [expected].
  * Detects cycles and DAG structure in Maps and Lists.
  */
 verifyGraph(expected, actual) {
   var eItems = [];
   var aItems = [];
 
   message(path, reason) => path == ''
       ? reason
       : reason == null ? "path: $path" : "path: $path, $reason";
 
   walk(path, expected, actual) {
     if (expected is String || expected is num || expected == null) {
       Expect.equals(expected, actual, message(path, 'not equal'));
       return;
     }
 
     // Cycle or DAG?
     for (int i = 0; i < eItems.length; i++) {
       if (expected === eItems[i]) {
-        Expect.identical(aItems[i], actual, message(path, 'back or side edge'));
+        Expect.identical(aItems[i], actual,
+                         message(path, 'missing back or side edge'));
         return;
       }
     }
+    for (int i = 0; i < aItems.length; i++) {
+      if (actual === aItems[i]) {
+        Expect.identical(eItems[i], expected,
+                         message(path, 'extra back or side edge'));
+        return;
+      }
+    }
     eItems.add(expected);
     aItems.add(actual);
 
     if (expected is List) {
       Expect.isTrue(actual is List, message(path, '$actual is List'));
       Expect.equals(expected.length, actual.length,
                     message(path, 'different list lengths'));
       for (var i = 0; i < expected.length; i++) {
         walk('$path[$i]', expected[i], actual[i]);
       }
@@ skipping 14 matching lines @@
         }
       }
       return;
     }
 
     Expect.fail('Unhandled type: $expected');
   }
 
   walk('', expected, actual);
 }