Add CoreClasses

pkg/compiler/lib/src/cps_ir/cps_ir_builder_task.dart

 // Copyright (c) 2013, 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.ir_builder_task;
 
 import '../closure.dart' as closurelib;
 import '../closure.dart' hide ClosureScope;
 import '../common.dart';
 import '../common/names.dart' show
@@ skipping 2478 matching lines @@
   bool requiresRuntimeTypesFor(ClassElement cls) {
     return cls.typeVariables.isNotEmpty && _backend.classNeedsRti(cls);
   }
 
   FunctionElement get stringifyFunction {
     return _backend.helpers.stringInterpolationHelper;
   }
 
   FunctionElement get throwTypeErrorHelper => _backend.helpers.throwTypeError;
 
-  ClassElement get nullClass => _compiler.nullClass;
+  ClassElement get nullClass => _compiler.coreClasses.nullClass;
 
   DartType unaliasType(DartType type) => type.unaliased;
 
   TypeMask getTypeMaskForForeign(NativeBehavior behavior) {
     if (behavior == null) {
       return _backend.dynamicType;
     }
     return TypeMaskFactory.fromNativeBehavior(behavior, _compiler);
   }
 
@@ skipping 1069 matching lines @@
     if (compiler.backend.isForeign(function)) {
       return handleForeignCode(node, function, argumentList, callStructure);
     } else {
       return irBuilder.buildStaticFunctionInvocation(function, callStructure,
           translateStaticArguments(argumentList, function, callStructure),
           sourceInformation:
               sourceInformationBuilder.buildCall(node, node.selector));
     }
   }
 }