Run closed_world2_test using the normal compiler pipeline.

tests/compiler/dart2js/mock_compiler.dart

 // Copyright (c) 2016, 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 'dart:async';
 import 'dart:collection';
 
 import 'package:compiler/compiler_new.dart' as api;
@@ skipping 191 matching lines @@
         diagnosticHandler.report(message.message, uri, begin, end, text, kind);
       }
     }
 
     processMessage(message, kind);
     infoMessages.forEach((i) => processMessage(i, api.Diagnostic.INFO));
   }
 
   CollectingTreeElements resolveStatement(String text) {
     parsedTree = parseStatement(text);
-    return resolveNodeStatement(parsedTree, new MockElement(mainApp));
+    LibraryElement library = mainApp;
+    return resolveNodeStatement(parsedTree, new MockElement(library));
   }
 
   TreeElementMapping resolveNodeStatement(
       Node tree, ExecutableElement element) {
     ResolverVisitor visitor = new ResolverVisitor(
         this.resolution,
         element,
         new ResolutionRegistry(
             this.backend.target, new CollectingTreeElements(element)),
         scope:
             new MockTypeVariablesScope(element.enclosingElement.buildScope()));
     if (visitor.scope is LibraryScope ||
         visitor.scope is MockTypeVariablesScope) {
       visitor.scope = new MethodScope(visitor.scope, element);
     }
     visitor.visit(tree);
     visitor.scope = new LibraryScope(element.library);
     return visitor.registry.mapping;
   }
 
   resolverVisitor() {
-    Element mockElement = new MockElement(mainApp.entryCompilationUnit);
+    LibraryElement library = mainApp;
+    Element mockElement = new MockElement(library.entryCompilationUnit);
     ResolverVisitor visitor = new ResolverVisitor(
         this.resolution,
         mockElement,
         new ResolutionRegistry(
             this.backend.target, new CollectingTreeElements(mockElement)),
         scope: mockElement.enclosingElement.buildScope());
     visitor.scope = new MethodScope(visitor.scope, mockElement);
     return visitor;
   }
 
@@ skipping 145 matching lines @@
       trustTypeAnnotations: trustTypeAnnotations,
       enableTypeAssertions: enableTypeAssertions,
       enableUserAssertions: enableUserAssertions,
       expectedErrors: expectedErrors,
       expectedWarnings: expectedWarnings,
       outputProvider: outputProvider);
   compiler.registerSource(uri, code);
   compiler.diagnosticHandler = createHandler(compiler, code);
   return compiler;
 }