Improve the performance of closure-converted code.

pkg/kernel/lib/transformations/closure/context.dart

 // Copyright (c) 2016, 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 kernel.transformations.closure.context;
 
 import '../../ast.dart'
     show
         Expression,
+        FunctionNode,
         NullLiteral,
         StringLiteral,
         Throw,
         TreeNode,
         VariableDeclaration,
         VariableGet,
         VariableSet,
         VectorCreation,
         VectorGet,
         VectorSet,
@@ skipping 110 matching lines @@
 
   void extend(VariableDeclaration variable, Expression value) {
     // Increase index by 2, because the type arguments vector occupies position
     // 0, the parent occupies position 1, and all other variables are therefore
     // shifted by 2.
     VectorSet initializer =
         new VectorSet(expression, variables.length + 2, value);
     value.parent = initializer;
 
     converter.rewriter.insertExtendContext(initializer);
+    if (variable.parent is FunctionNode) {
+      converter.rewriter.insertZeroOutParameter(variable);
+    }
 
     ++vectorCreation.length;
     variables.add(variable);
     initializers[variable] = initializer;
   }
 
   void update(VariableDeclaration variable, Expression value) {
     VectorSet initializer = initializers[variable];
     initializer.value = value;
     value.parent = initializer;
@@ skipping 88 matching lines @@
       // Item 1 of a context always points to its parent.
       context = new VectorGet(context, 1);
     }
     throw 'Unbound NestedContext.lookup($variable)';
   }
 
   Context toNestedContext([Accessor accessor]) {
     return new NestedContext(converter, accessor ?? this.accessor, variabless);
   }
 }