Minor fixes to for-loop type inference

pkg/front_end/lib/src/fasta/kernel/body_builder.dart

Index: pkg/front_end/lib/src/fasta/kernel/body_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/body_builder.dart b/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
index 351dae1409b48ac77cb3c4fed76bb41f994d9fad..3286804538554562c3ca45baa6a3f8894282a2dd 100644
--- a/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
@@ -1494,7 +1494,7 @@ class BodyBuilder extends ScopeListener<JumpTarget> implements BuilderHelper {
     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);