Store constant variable initializers in elements.

pkg/compiler/lib/src/elements/modelx.dart

 // Copyright (c) 2013, 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 elements.modelx;
 
 import '../common.dart';
 import '../common/resolution.dart' show Resolution, ParsingContext;
 import '../compiler.dart' show Compiler;
 import '../constants/constant_constructors.dart';
@@ skipping 1379 matching lines @@
 }
 
 abstract class ConstantVariableMixin implements VariableElement {
   ConstantExpression constantCache;
 
   ConstantExpression get constant {
     if (isPatch) {
       ConstantVariableMixin originVariable = origin;
       return originVariable.constant;
     }
-    assert(invariant(this, constantCache != null,
+    assert(invariant(this, !isConst || constantCache != null,
         message: "Constant has not been computed for $this."));
     return constantCache;
   }
 
   void set constant(ConstantExpression value) {
     if (isPatch) {
       ConstantVariableMixin originVariable = origin;
       originVariable.constant = value;
       return;
     }
@@ skipping 1863 matching lines @@
     if (definingElement.isField) {
       FieldElement field = definingElement;
       body = field.initializer;
     } else if (node != null && node.asFunctionExpression() != null) {
       body = node.asFunctionExpression().body;
     }
     return new ParsedResolvedAst(
         declaration, node, body, definingElement.treeElements);
   }
 }