Forget elements from resolution also.

pkg/compiler/lib/src/common/resolution.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 dart2js.common.resolution;
 
 import '../common.dart';
 import '../compiler.dart' show
     Compiler;
@@ skipping 168 matching lines @@
   void resolveTypedef(TypedefElement typdef);
   void resolveClass(ClassElement cls);
   void registerClass(ClassElement cls);
   void resolveMetadataAnnotation(MetadataAnnotation metadataAnnotation);
   FunctionSignature resolveSignature(FunctionElement function);
   DartType resolveTypeAnnotation(Element element, TypeAnnotation node);
 
   bool hasBeenResolved(Element element);
   WorldImpact getWorldImpact(Element element);
   WorldImpact computeWorldImpact(Element element);
+  void forgetElement(Element element);
 }
 
 // TODO(johnniwinther): Rename to `Parser` or `ParsingContext`.
 abstract class Parsing {
   DiagnosticReporter get reporter;
   void parsePatchClass(ClassElement cls);
   measure(f());
   ScannerOptions getScannerOptionsFor(Element element);
 }