Remove unused code for StringConcatNode from the AST and the graph builder.

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 140 matching lines @@
 void AstPrinter::VisitComparisonNode(ComparisonNode* node) {
   VisitGenericAstNode(node);
 }
 
 
 void AstPrinter::VisitBinaryOpNode(BinaryOpNode* node) {
   VisitGenericAstNode(node);
 }
 
 
-void AstPrinter::VisitStringConcatNode(StringConcatNode* node) {
-  VisitGenericAstNode(node);
-}
-
-
 void AstPrinter::VisitUnaryOpNode(UnaryOpNode* node) {
   VisitGenericAstNode(node);
 }
 
 
 void AstPrinter::VisitConditionalExprNode(ConditionalExprNode* node) {
   VisitGenericAstNode(node);
 }
 
 
@@ skipping 301 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