Add Closure call method to created closure class

pkg/compiler/lib/src/js_model/closure_visitors.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:kernel/ast.dart' as ir;
 
 import '../closure.dart';
 import 'closure.dart';
 
 /// This builder walks the code to determine what variables are captured/free at
 /// various points to build CapturedScope that can respond to queries
 /// about how a particular variable is being used at any point in the code.
 class CapturedScopeBuilder extends ir.Visitor {
   ir.TreeNode _currentLocalFunction;
 
   ClosureModel _model;
 
   /// A map of each visited call node with the associated information about what
   /// variables are captured/used. Each ir.Node key corresponds to a scope that
   /// was encountered while visiting a closure (initially called through
   /// [translateLazyIntializer] or [translateConstructorOrProcedure]).
   Map<ir.Node, KernelCapturedScope> get _scopesCapturedInClosureMap =>
       _model.capturedScopesMap;
 
   /// A map of the nodes that we have flagged as necessary to generate closure
   /// classes for in a later stage. We map that node to information ascertained
   /// about variable usage in the surrounding scope.
-  Map<ir.TreeNode /* ir.Field | ir.FunctionNode */, KernelScopeInfo>
-      get _closuresToGenerate => _model.closuresToGenerate;
+  Map<ir.FunctionNode, KernelScopeInfo> get _closuresToGenerate =>
+      _model.closuresToGenerate;
 
   /// The local variables that have been declared in the current scope.
   List<ir.VariableDeclaration> _scopeVariables;
 
   /// Pointer to the context in which this closure is executed.
   /// For example, in the expression `var foo = () => 3 + i;`, the executable
   /// context as we walk the nodes in that expression is the ir.Field `foo`.
   ir.Node _executableContext;
 
   /// A flag to indicate if we are currently inside a closure.
@@ skipping 218 matching lines @@
   }
 
   void translateConstructorOrProcedure(ir.Node constructorOrProcedure) {
     constructorOrProcedure.accept(this);
   }
 
   void visitFunctionNode(ir.FunctionNode functionNode) {
     visitInvokable(functionNode);
   }
 }