Revert "Move dart2js from sdk/lib/_internal/compiler to pkg/compiler"

pkg/compiler/lib/src/elements/visitor.dart

-// 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.
-
-library visitor;
-
-import 'elements.dart';
-import '../closure.dart'
-    show BoxFieldElement,
-         ClosureClassElement,
-         ClosureFieldElement;
-
-abstract class ElementVisitor<R> {
-  R visit(Element e) => e.accept(this);
-
-  R visitElement(Element e);
-  R visitErroneousElement(ErroneousElement e) => visitFunctionElement(e);
-  R visitWarnOnUseElement(WarnOnUseElement e) => visitElement(e);
-  R visitAmbiguousElement(AmbiguousElement e) => visitElement(e);
-  R visitScopeContainerElement(ScopeContainerElement e) => visitElement(e);
-  R visitCompilationUnitElement(CompilationUnitElement e) => visitElement(e);
-  R visitLibraryElement(LibraryElement e) => visitScopeContainerElement(e);
-  R visitPrefixElement(PrefixElement e) => visitElement(e);
-  R visitTypedefElement(TypedefElement e) => visitElement(e);
-  R visitVariableElement(VariableElement e) => visitElement(e);
-  R visitParameterElement(ParameterElement e) => visitVariableElement(e);
-  R visitFormalElement(FormalElement e) => visitElement(e);
-  R visitFieldElement(FieldElement e) => visitVariableElement(e);
-  R visitFieldParameterElement(InitializingFormalElement e) =>
-      visitParameterElement(e);
-  R visitAbstractFieldElement(AbstractFieldElement e) => visitElement(e);
-  R visitFunctionElement(FunctionElement e) => visitElement(e);
-  R visitConstructorBodyElement(ConstructorBodyElement e) => visitElement(e);
-  R visitClassElement(ClassElement e) => visitScopeContainerElement(e);
-  R visitTypeDeclarationElement(TypeDeclarationElement e) => visitElement(e);
-  R visitMixinApplicationElement(MixinApplicationElement e) {
-    return visitClassElement(e);
-  }
-  R visitTypeVariableElement(TypeVariableElement e) => visitElement(e);
-  R visitBoxFieldElement(BoxFieldElement e) => visitElement(e);
-  R visitClosureClassElement(ClosureClassElement e) => visitClassElement(e);
-  R visitClosureFieldElement(ClosureFieldElement e) => visitVariableElement(e);
-}