Retain elements a finer granularity than library.

dart/tests/compiler/dart2js/mock_compiler.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 mock_compiler;
 
 import "package:expect/expect.dart";
 import 'dart:collection';
 
 import '../../../sdk/lib/_internal/compiler/compiler.dart' as api;
@@ skipping 322 matching lines @@
   bool get compilationFailed => !errors.isEmpty;
 
   void clearWarnings() {
     warnings = [];
   }
 
   void clearErrors() {
     errors = [];
   }
 
-  TreeElementMapping resolveStatement(String text) {
+  CollectingTreeElements resolveStatement(String text) {
     parsedTree = parseStatement(text);
     return resolveNodeStatement(parsedTree, mainApp);
   }
 
   TreeElementMapping resolveNodeStatement(Node tree, Element element) {
     ResolverVisitor visitor =
         new ResolverVisitor(this, element, new CollectingTreeElements(element));
     if (visitor.scope is LibraryScope) {
       visitor.scope = new MethodScope(visitor.scope, element);
     }
@@ skipping 19 matching lines @@
   }
 
   void scanBuiltinLibraries() {
     // Do nothing. The mock core library is already handled in the constructor.
   }
 
   LibraryElement scanBuiltinLibrary(String name) {
     // Do nothing. The mock core library is already handled in the constructor.
   }
 
-  void importCoreLibrary(LibraryElement library) {
-    scanner.importLibrary(library, coreLibrary, null);
-  }
-
   Uri translateResolvedUri(LibraryElement importingLibrary,
                            Uri resolvedUri, Node node) => resolvedUri;
 
   // The mock library doesn't need any patches.
   Uri resolvePatchUri(String dartLibraryName) => null;
 
   Script readScript(Uri uri, [Node node]) {
     SourceFile sourceFile = sourceFiles[uri.toString()];
     if (sourceFile == null) throw new ArgumentError(uri);
     return new Script(uri, sourceFile);
@@ skipping 23 matching lines @@
     fail('Too few warnings');
   }
   if (found.hasNext) {
     do {
       print('Additional warning "${found.next()}"');
     } while (found.hasNext);
     fail('Too many warnings');
   }
 }
 
-void importLibrary(LibraryElement target, LibraryElement imported,
+void importLibrary(LibraryElement target, LibraryElementX imported,
                    Compiler compiler) {
   for (var element in imported.localMembers) {
     compiler.withCurrentElement(element, () {
       target.addToScope(element, compiler);
     });
   }
 }
 
 LibraryElement mockLibrary(Compiler compiler, String source) {
   Uri uri = new Uri(scheme: "source");
@@ skipping 18 matching lines @@
   }
 }
 
 class MockDeferredLoadTask extends DeferredLoadTask {
   MockDeferredLoadTask(Compiler compiler) : super(compiler);
 
   void registerMainApp(LibraryElement mainApp) {
     // Do nothing.
   }
 }