Insert implicit downcasts in kernel strong mode.

pkg/kernel/lib/text/ast_to_text.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.ast_to_text;
 
 import '../ast.dart';
 import '../import_table.dart';
 import '../type_propagation/type_propagation.dart';
 
 class Namer<T> {
@@ skipping 965 matching lines @@
     writeSpaced('in');
     writeExpression(node.body);
   }
 
   defaultExpression(Expression node) {
     writeWord('${node.runtimeType}');
   }
 
   visitVariableGet(VariableGet node) {
     writeVariableReference(node.variable);
+    if (node.promotedType != null) {
+      writeSymbol('{');
+      writeNode(node.promotedType);
+      writeSymbol('}');
+      state = WORD;
+    }
   }
 
   visitVariableSet(VariableSet node) {
     writeVariableReference(node.variable);
     writeSpaced('=');
     writeExpression(node.value);
   }
 
   void writeInterfaceTarget(Name name, Member target) {
     if (target != null) {
@@ skipping 539 matching lines @@
   }
   throw 'illegal ProcedureKind: $kind';
 }
 
 class ExpressionPrinter {
   final Printer writeer;
   final int minimumPrecedence;
 
   ExpressionPrinter(this.writeer, this.minimumPrecedence);
 }