Make sure that libraries loaded from dart:core gets dart:core implicitly loaded.

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("dart:uri");
 
 #import("../../../lib/compiler/implementation/elements/elements.dart");
 #import("../../../lib/compiler/implementation/leg.dart");
@@ skipping 33 matching lines @@
   add$1(receiver, value) {}
   get$length(receiver) {}
   filter(receiver, predicate) {}
   removeLast(receiver) {}
   iterator(receiver) {}
   next(receiver) {}
   hasNext(receiver) {}''';
 
 final String DEFAULT_CORELIB = @'''
   print(var obj) {}
+  assert(x) {}
   interface int extends num {}
   interface double extends num {}
   class bool {}
   class String {}
   class Object {}
   interface num {}
   class Function {}
   class List {}
   class Closure {}
   class Null {}
   class Dynamic {}''';
 
 class MockCompiler extends Compiler {
   List<WarningMessage> warnings;
   List<WarningMessage> errors;
   final Map<String, SourceFile> sourceFiles;
   Node parsedTree;
 
   MockCompiler([String coreSource = DEFAULT_CORELIB,
                 String helperSource = DEFAULT_HELPERLIB,
                 String interceptorsSource = DEFAULT_INTERCEPTORSLIB])
       : warnings = [], errors = [],
         sourceFiles = new Map<String, SourceFile>(),
         super() {
     Uri uri = new Uri.fromComponents(scheme: "source");
     var script = new Script(uri, new MockFile(coreSource));
     coreLibrary = new LibraryElement(script);
     parseScript(coreSource, coreLibrary);
+    // We need to set the assert method to avoid calls with a 'null'
+    // target being interpreted as a call to assert.
+    assertMethod = coreLibrary.find(buildSourceString('assert'));
 
     script = new Script(uri, new MockFile(helperSource));
     jsHelperLibrary = new LibraryElement(script);
     parseScript(helperSource, jsHelperLibrary);
 
     script = new Script(uri, new MockFile(interceptorsSource));
     interceptorsLibrary = new LibraryElement(script);
     parseScript(interceptorsSource, interceptorsLibrary);
 
-    scanner.importLibrary(jsHelperLibrary, coreLibrary, null);
-    scanner.importLibrary(interceptorsLibrary, coreLibrary, null);
     mainApp = mockLibrary(this, "");
     initializeSpecialClasses();
   }
 
   void reportWarning(Node node, var message) {
     warnings.add(new WarningMessage(node, message.message));
   }
 
   void reportError(Node node, var message) {
     if (message is String && message.startsWith("no #library tag found in")) {
       // TODO(ahe): Fix the MockCompiler to not have this problem.
       return;
     }
     errors.add(new WarningMessage(node, message.message));
   }
 
   void reportMessage(SourceSpan span, var message, api.Diagnostic kind) {
     var diagnostic = new WarningMessage(null, message.message);
     if (kind === api.Diagnostic.ERROR) {
       errors.add(diagnostic);
     } else {
       warnings.add(diagnostic);
     }
   }
 
   void reportDiagnostic(SourceSpan span, String message, var kind) {
     print(message);
   }
 
+  bool get compilationFailed => !errors.isEmpty();
+
   void clearWarnings() {
     warnings = [];
   }
 
   void clearErrors() {
     errors = [];
   }
 
   TreeElementMapping resolveStatement(String text) {
     parsedTree = parseStatement(text);
@@ skipping 24 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);
+  }
+
   // The mock library doesn't need any patches.
   Uri resolvePatchUri(String dartLibraryName) => null;
 
   Script readScript(Uri uri, [ScriptTag node]) {
     SourceFile sourceFile = sourceFiles[uri.toString()];
     if (sourceFile === null) throw new IllegalArgumentException(uri);
     return new Script(uri, sourceFile);
   }
 }
 
@@ skipping 26 matching lines @@
     });
   }
 }
 
 LibraryElement mockLibrary(Compiler compiler, String source) {
   Uri uri = new Uri.fromComponents(scheme: "source");
   var library = new LibraryElement(new Script(uri, new MockFile(source)));
   importLibrary(library, compiler.coreLibrary, compiler);
   return library;
 }