Add more tested features to closure_test

tests/compiler/dart2js/equivalence/id_equivalence.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.
 
 import 'package:compiler/src/elements/elements.dart';
 import 'package:compiler/src/resolution/access_semantics.dart';
 import 'package:compiler/src/resolution/send_structure.dart';
 import 'package:compiler/src/resolution/tree_elements.dart';
 import 'package:compiler/src/tree/nodes.dart' as ast;
 import 'package:kernel/ast.dart' as ir;
@@ skipping 195 matching lines @@
   Id computeNodeId(ir.TreeNode node) {
     if (node is ir.MethodInvocation) {
       assert(node.fileOffset != ir.TreeNode.noOffset);
       return new NodeId(node.fileOffset);
     } else if (node is ir.PropertyGet) {
       assert(node.fileOffset != ir.TreeNode.noOffset);
       return new NodeId(node.fileOffset);
     } else if (node is ir.VariableDeclaration) {
       assert(node.fileOffset != ir.TreeNode.noOffset);
       return new NodeId(node.fileOffset);
+      // TODO(johnniwinther): Enable when function expressions have offsets.
+      /*} else if (node is ir.FunctionExpression) {
+      assert(node.fileOffset != ir.TreeNode.noOffset);
+      return new NodeId(node.fileOffset);*/
     } else if (node is ir.FunctionDeclaration) {
       assert(node.fileOffset != ir.TreeNode.noOffset);
       return new NodeId(node.fileOffset);
     }
     return null;
   }
 }
 
 /// Visitor that finds the IR node corresponding to an [Id].
 class IrIdFinder extends ir.Visitor with IrEnumeratorMixin {
@@ skipping 24 matching lines @@
     if (found == null) {
       Id id = computeElementId(node);
       if (id == soughtId) {
         found = node;
         return;
       }
       defaultTreeNode(node);
     }
   }
 }