Compute constants from IR nodes

pkg/compiler/lib/src/kernel/element_map_impl.dart

 // Copyright (c) 2017, 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.kernel.element_map;
 
 import 'package:kernel/ast.dart' as ir;
 import 'package:kernel/clone.dart';
 import 'package:kernel/type_algebra.dart';
 
@@ skipping 112 matching lines @@
   ElementEnvironment get elementEnvironment => _elementEnvironment;
 
   ConstantEnvironment get constantEnvironment => _constantEnvironment;
 
   DartTypes get types => _types;
 
   @override
   native.BehaviorBuilder get nativeBehaviorBuilder => _nativeBehaviorBuilder;
 
   @override
-  ConstantValue computeConstantValue(ConstantExpression constant) {
+  ConstantValue computeConstantValue(ConstantExpression constant,
+      {bool requireConstant: true}) {
     return _constantEnvironment.getConstantValue(constant);
   }
 
   LibraryEntity lookupLibrary(Uri uri) {
     _KLibraryEnv libraryEnv = _env.lookupLibrary(uri);
     if (libraryEnv == null) return null;
     return _getLibrary(libraryEnv.library, libraryEnv);
   }
 
   KLibrary _getLibrary(ir.Library node, [_KLibraryEnv libraryEnv]) {
@@ skipping 1403 matching lines @@
     return node.isExternal &&
         !elementMap.isForeignLibrary(node.enclosingLibrary);
   }
 
   @override
   bool isJsInteropMember(MemberEntity element) {
     // TODO(johnniwinther): Compute this.
     return false;
   }
 }