Refactor DartTypeVisitor and ElementVisitor.

pkg/compiler/lib/src/js_backend/constant_handler_javascript.dart

 // Copyright (c) 2014, 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.
 
 part of js_backend;
 
 /// [ConstantCompilerTask] for compilation of constants for the JavaScript
 /// backend.
 ///
 /// Since this task needs to distinguish between frontend and backend constants
@@ skipping 195 matching lines @@
   ConstantExpression createTypeConstant(TypeDeclarationElement element) {
     DartType elementType = element.rawType;
     DartType constantType =
         compiler.backend.typeImplementation.computeType(compiler);
     return new TypeConstantExpression(
         new TypeConstantValue(elementType, constantType), elementType);
   }
 
   void forgetElement(Element element) {
     super.forgetElement(element);
-    element.accept(new ForgetConstantElementVisitor(this));
+    const ForgetConstantElementVisitor().visit(element, this);
     if (element is AstElement && element.hasNode) {
       element.node.accept(new ForgetConstantNodeVisitor(this));
     }
   }
 }
 
-class ForgetConstantElementVisitor extends ElementVisitor {
-  final JavaScriptConstantCompiler constants;
+class ForgetConstantElementVisitor
+    extends BaseElementVisitor<dynamic, JavaScriptConstantCompiler> {
+  const ForgetConstantElementVisitor();
 
-  ForgetConstantElementVisitor(this.constants);
-
-  void visitElement(Element e) {
+  void visitElement(Element e, JavaScriptConstantCompiler constants) {
     for (MetadataAnnotation data in e.metadata) {
       constants.metadataConstantMap.remove(data);
       if (data.hasNode) {
         data.node.accept(new ForgetConstantNodeVisitor(constants));
       }
     }
   }
 
-  void visitFunctionElement(FunctionElement e) {
-    super.visitFunctionElement(e);
+  void visitFunctionElement(FunctionElement e,
+                            JavaScriptConstantCompiler constants) {
+    super.visitFunctionElement(e, constants);
     if (e.hasFunctionSignature) {
-      e.functionSignature.forEachParameter(this.visit);
+      e.functionSignature.forEachParameter((p) => visit(p, constants));
     }
   }
 }
 
 class ForgetConstantNodeVisitor extends Visitor {
   final JavaScriptConstantCompiler constants;
 
   ForgetConstantNodeVisitor(this.constants);
 
   void visitNode(Node node) {
     node.visitChildren(this);
     constants.nodeConstantMap.remove(node);
 
     // TODO(ahe): This doesn't belong here. Rename this class and generalize.
     var closureClassMap =
         constants.compiler.closureToClassMapper.closureMappingCache
         .remove(node);
     if (closureClassMap != null) {
       closureClassMap.removeMyselfFrom(
           constants.compiler.enqueuer.codegen.universe);
     }
   }
 }