Store constant variable initializers in elements.

tests/compiler/dart2js/serialization_test_helper.dart

Index: tests/compiler/dart2js/serialization_test_helper.dart
diff --git a/tests/compiler/dart2js/serialization_test_helper.dart b/tests/compiler/dart2js/serialization_test_helper.dart
index 4ee842de3f6ac012e3e748a767915331f31a2ad7..0c871a8de2e66c370d79693c42ec4ca52f36409b 100644
--- a/tests/compiler/dart2js/serialization_test_helper.dart
+++ b/tests/compiler/dart2js/serialization_test_helper.dart
@@ -105,8 +105,12 @@ bool check(var object1, var object2, String property, var value1, var value2,
            [bool equivalence(a, b) = equality]) {
   if (!equivalence(value1, value2)) {
     throw "property='$property'\n "
-          "object1=$object1 (${object1.runtimeType})\n value='${value1}' <>\n "
-          "object2=$object2 (${object2.runtimeType})\n value='${value2}'";
+          "object1=$object1 (${object1.runtimeType})\n "
+          "value=${value1 == null ? "null" : "'$value1'"} "
+          "(${value1.runtimeType}) <>\n "
+          "object2=$object2 (${object2.runtimeType})\n "
+          "value=${value2 == null ? "null" : "'$value2'"} "
+          "(${value2.runtimeType})";
   }
   return true;
 }