Store constant variable initializers in elements.

tests/compiler/dart2js/serialization_test_helper.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library dart2js.serialization_test_helper;
 
 import 'dart:io';
 import 'memory_compiler.dart';
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/common/resolution.dart';
@@ skipping 87 matching lines @@
     return checkConstantLists(object1, object2, property, list1, list2);
   }
 }
 
 /// Check that the values [property] of [object1] and [object2], [value1] and
 /// [value2] respectively, are equal and throw otherwise.
 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;
 }
 
 /// Check equivalence of the two lists, [list1] and [list2], using
 /// [checkEquivalence] to check the pair-wise equivalence.
 ///
 /// Uses [object1], [object2] and [property] to provide context for failures.
 bool checkListEquivalence(
     Object object1, Object object2, String property,
@@ skipping 249 matching lines @@
 
   if (impact1 == null) {
     throw 'Missing impact for $member1. $member2 has $impact2';
   }
   if (impact2 == null) {
     throw 'Missing impact for $member2. $member1 has $impact1';
   }
 
   testResolutionImpactEquivalence(impact1, impact2, const CheckStrategy());
 }