Minor fixes to for-loop type inference

pkg/front_end/lib/src/fasta/kernel/body_builder.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 fasta.body_builder;
 
 import '../fasta_codes.dart'
     show
         FastaMessage,
         codeConstFieldWithoutInitializer,
@@ skipping 1476 matching lines @@
     exitLocalScope();
     JumpTarget continueTarget = exitContinueTarget();
     JumpTarget breakTarget = exitBreakTarget();
     if (continueTarget.hasUsers) {
       body = new KernelLabeledStatement(body);
       continueTarget.resolveContinues(body);
     }
     Statement result =
         new KernelForStatement(variables, condition, updates, body);
     if (begin != null) {
-      result = new Block(<Statement>[begin, result]);
+      result = new KernelBlock(<Statement>[begin, result]);
     }
     if (breakTarget.hasUsers) {
       result = new KernelLabeledStatement(result);
       breakTarget.resolveBreaks(result);
     }
     exitLoopOrSwitch(result);
   }
 
   @override
   void endAwaitExpression(Token keyword, Token endToken) {
@@ skipping 2164 matching lines @@
     if (starToken == null) {
       return AsyncMarker.Async;
     } else {
       assert(identical(starToken.stringValue, "*"));
       return AsyncMarker.AsyncStar;
     }
   } else {
     return internalError("Unknown async modifier: $asyncToken");
   }
 }