Fix Token::kAS and its printing according to Regis' comment.

runtime/vm/ast_printer.cc

 // Copyright (c) 2011, 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.
 
 #include "vm/ast_printer.h"
 
 #include "vm/handles.h"
 #include "vm/object.h"
 #include "vm/os.h"
 #include "vm/parser.h"
@@ skipping 139 matching lines @@
 }
 
 
 void AstPrinter::VisitPrimaryNode(PrimaryNode* node) {
   OS::Print("***** PRIMARY NODE IN AST ***** (%s '%s')",
       node->Name(), node->primary().ToCString());
 }
 
 
 void AstPrinter::VisitComparisonNode(ComparisonNode* node) {
-  VisitGenericAstNode(node);
+  if (node->kind() == Token::kAS) {
+    OS::Print("(as ");
+    node->VisitChildren(this);
+    OS::Print(")");
+  } else {
+    VisitGenericAstNode(node);
+  }
 }
 
 
 void AstPrinter::VisitBinaryOpNode(BinaryOpNode* node) {
   VisitGenericAstNode(node);
 }
 
 
 void AstPrinter::VisitUnaryOpNode(UnaryOpNode* node) {
   VisitGenericAstNode(node);
@@ skipping 313 matching lines @@
   ASSERT(node_sequence != NULL);
   AstPrinter ast_printer;
   const char* function_name =
       parsed_function.function().ToFullyQualifiedCString();
   OS::Print("Ast for function '%s' {\n", function_name);
   node_sequence->Visit(&ast_printer);
   OS::Print("}\n");
 }
 
 }  // namespace dart