Add support for converted closures with explicit contexts to VM

pkg/kernel/lib/transformations/closure/rewriter.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 kernel.transformations.closure.rewriter;
 
 import '../../ast.dart';
 import 'converter.dart' show ClosureConverter;
 
 /// Used by the [Context] to initialize and update the context variable
@@ skipping 33 matching lines @@
 class BlockRewriter extends AstRewriter {
   Block _currentBlock;
   int _insertionIndex;
 
   BlockRewriter(this._currentBlock) : _insertionIndex = 0;
 
   BlockRewriter forNestedBlock(Block block) {
     return _currentBlock != block ? new BlockRewriter(block) : this;
   }
 
-  void transformStatements(Block block, ClosureConverter converter) {
+  void transformStatements(ClosureConverter converter) {
     while (_insertionIndex < _currentBlock.statements.length) {
       var original = _currentBlock.statements[_insertionIndex];
       var transformed = original.accept(converter);
       assert(_currentBlock.statements[_insertionIndex] == original);
       if (transformed == null) {
         _currentBlock.statements.removeAt(_insertionIndex);
       } else {
         _currentBlock.statements[_insertionIndex++] = transformed;
         transformed.parent = _currentBlock;
       }
@@ skipping 46 matching lines @@
 
   @override
   void insertExtendContext(VectorSet extender) {
     Let parent = initializingExpression.parent;
     Let binding = new Let(new VariableDeclaration(null, initializer: extender),
         initializingExpression);
     parent.body = binding;
     binding.parent = parent;
   }
 }