dart2js: Use an abstract Name class for names in the generated JavaScript ast.

pkg/compiler/lib/src/js_emitter/code_emitter_task.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.
 
 part of dart2js.js_emitter;
 
 const USE_NEW_EMITTER = const bool.fromEnvironment("dart2js.use.new.emitter");
 
 /**
  * Generates the code for all used classes in the program. Static fields (even
@@ skipping 198 matching lines @@
                 backend.retainMetadataOf);
           }
         }
       }
       for (ClassElement cls in neededClasses) {
         final onlyForRti = typeTestRegistry.rtiNeededClasses.contains(cls);
         if (!onlyForRti) {
           backend.retainMetadataOf(cls);
           oldEmitter.classEmitter.visitFields(cls, false,
               (Element member,
-               String name,
-               String accessorName,
+               jsAst.Name name,
+               jsAst.Name accessorName,
                bool needsGetter,
                bool needsSetter,
                bool needsCheckedSetter) {
             bool needsAccessor = needsGetter || needsSetter;
             if (needsAccessor && backend.isAccessibleByReflection(member)) {
               backend.retainMetadataOf(member);
             }
           });
         }
       }
@@ skipping 222 matching lines @@
   bool isConstantInlinedOrAlreadyEmitted(ConstantValue constant);
 
   /// Returns the JS code for accessing the given [constant].
   jsAst.Expression constantReference(ConstantValue constant);
 
   /// Returns the JS template for the given [builtin].
   jsAst.Template templateForBuiltin(JsBuiltin builtin);
 
   void invalidateCaches();
 }