Remove code supporting incremental compilation in dart2js

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

 // 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.
 
 library js_backend.namer;
 
 import 'dart:collection' show HashMap;
 
 import 'package:js_runtime/shared/embedded_names.dart' show JsGetName;
 
@@ skipping 1693 matching lines @@
     } else if (name == '|') {
       return r'$or';
     } else if (name == '-') {
       return r'$sub';
     } else if (name == 'unary-') {
       return r'$negate';
     } else {
       return name;
     }
   }
-
-  String get incrementalHelperName => r'$dart_unsafe_incremental_support';
-
-  jsAst.Expression get accessIncrementalHelper {
-    return js('self.${incrementalHelperName}');
-  }
-
-  void forgetElement(Element element) {
-    jsAst.Name globalName = userGlobals[element];
-    invariant(element, globalName != null, message: 'No global name.');
-    userGlobals.remove(element);
-  }
 }
 
 /**
  * Generator of names for [ConstantValue] values.
  *
  * The names are stable under perturbations of the source.  The name is either a
  * short sequence of words, if this can be found from the constant, or a type
  * followed by a hash tag.
  *
  *     List_imX                // A List, with hash tag.
@@ skipping 469 matching lines @@
   void addSuggestion(String original, String suggestion) {
     assert(!_suggestedNames.containsKey(original));
     _suggestedNames[original] = suggestion;
   }
 
   bool hasSuggestion(String original) => _suggestedNames.containsKey(original);
   bool isSuggestion(String candidate) {
     return _suggestedNames.containsValue(candidate);
   }
 }