Use computeConstantValue instead of constantValue

pkg/dev_compiler/lib/src/compiler/side_effect_analysis.dart

 // Copyright (c) 2015, 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.
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/src/generated/constant.dart';
 import 'package:analyzer/error/listener.dart'
     show AnalysisErrorListener, ErrorReporter;
@@ skipping 106 matching lines @@
   // TODO(jmesserly): this is used to determine if the field initialization is
   // side effect free. We should make the check more general, as things like
   // list/map literals/regexp are also side effect free and fairly common
   // to use as field initializers.
   bool isFieldInitConstant(VariableDeclaration field) =>
       field.initializer == null || computeConstant(field) != null;
 
   DartObject computeConstant(VariableDeclaration field) {
     // If the constant is already computed by ConstantEvaluator, just return it.
     VariableElement element = field.element;
-    var result = element.constantValue;
+    var result = element.computeConstantValue();
     if (result != null) return result;
 
     // ConstantEvaluator will not compute constants for non-const fields,
     // so run ConstantVisitor for those to figure out if the initializer is
     // actually a constant (and therefore side effect free to evaluate).
     assert(!field.isConst);
 
     var initializer = field.initializer;
     if (initializer == null) return null;
     return initializer.accept(constantVisitor);
   }
 }