Refactor ConstantSystem

tests/compiler/dart2js/constant_expression_evaluate_test.dart

Index: tests/compiler/dart2js/constant_expression_evaluate_test.dart
diff --git a/tests/compiler/dart2js/constant_expression_evaluate_test.dart b/tests/compiler/dart2js/constant_expression_evaluate_test.dart
index aa648eb2298a382787fcf45e1a2465a806293d19..3a3a6851909954affd51fa96112479317fa0ed43 100644
--- a/tests/compiler/dart2js/constant_expression_evaluate_test.dart
+++ b/tests/compiler/dart2js/constant_expression_evaluate_test.dart
@@ -7,12 +7,14 @@ library dart2js.constants.expressions.evaluate_test;
 import 'dart:async';
 import 'package:async_helper/async_helper.dart';
 import 'package:expect/expect.dart';
+import 'package:compiler/src/common/backend_api.dart';
 import 'package:compiler/src/constants/constructors.dart';
 import 'package:compiler/src/constants/evaluation.dart';
 import 'package:compiler/src/constants/expressions.dart';
 import 'package:compiler/src/constants/values.dart';
 import 'package:compiler/src/constant_system_dart.dart';
 import 'package:compiler/src/compiler.dart';
+import 'package:compiler/src/core_types.dart';
 import 'package:compiler/src/elements/elements.dart';
 import 'package:compiler/src/elements/resolution_types.dart';
 import 'memory_compiler.dart';
@@ -38,10 +40,10 @@ class ConstantData {
 }
 
 class MemoryEnvironment implements Environment {
-  final Compiler compiler;
+  final Compiler _compiler;
   final Map<String, String> env;
 
-  MemoryEnvironment(this.compiler, [this.env = const <String, String>{}]);
+  MemoryEnvironment(this._compiler, [this.env = const <String, String>{}]);
 
   @override
   String readFromEnvironment(String name) => env[name];
@@ -66,6 +68,12 @@ class MemoryEnvironment implements Environment {
   ConstantExpression getLocalConstant(LocalVariableElement local) {
     return local.constant;
   }
+
+  @override
+  CommonElements get commonElements => _compiler.commonElements;
+
+  @override
+  BackendClasses get backendClasses => _compiler.backend.backendClasses;
 }
 
 const List<TestData> DATA = const [