Accept constant string concatenation and constant string length as constant

runtime/vm/ast.h

 // Copyright (c) 2012, 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.
 
 #ifndef VM_AST_H_
 #define VM_AST_H_
 
 #include "platform/assert.h"
 #include "vm/allocation.h"
 #include "vm/growable_array.h"
@@ skipping 1405 matching lines @@
 
   AstNode* receiver() const { return receiver_; }
   const String& field_name() const { return field_name_; }
 
   virtual void VisitChildren(AstNodeVisitor* visitor) const {
     receiver()->Visit(visitor);
   }
 
   virtual AstNode* MakeAssignmentNode(AstNode* rhs);
 
+  virtual bool IsPotentiallyConst() const;
+  virtual const Instance* EvalConstExpr() const;
+
   DECLARE_COMMON_NODE_FUNCTIONS(InstanceGetterNode);
 
  private:
   AstNode* receiver_;
   const String& field_name_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(InstanceGetterNode);
 };
 
 
@@ skipping 468 matching lines @@
   const intptr_t try_index_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(InlinedFinallyNode);
 };
 
 }  // namespace dart
 
 #undef DECLARE_COMMON_NODE_FUNCTIONS
 
 #endif  // VM_AST_H_