Use LibraryIndex in CoreTypes instead of extending it.

pkg/kernel/lib/transformations/mixin_full_resolution.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 kernel.transformations.mixin_full_resolution;
 
 import '../ast.dart';
 import '../class_hierarchy.dart';
 import '../clone.dart';
 import '../core_types.dart';
 import '../target/targets.dart' show NoneTarget, Target;
@@ skipping 261 matching lines @@
       return new DirectMethodInvocation(
           new ThisExpression(), noSuchMethod, new Arguments([invocationPrime]))
         ..fileOffset = node.fileOffset;
     }
   }
 
   /// Creates an "new _InvocationMirror(...)" invocation.
   ConstructorInvocation _createInvocation(String methodName,
       Arguments callArguments, bool isSuperInvocation, Expression receiver) {
     if (_invocationMirrorConstructor == null) {
-      Class clazz = coreTypes.getClass('dart:core', '_InvocationMirror');
+      Class clazz = coreTypes.invocationMirrorClass;
       _invocationMirrorConstructor = clazz.constructors[0];
     }
 
     return targetInfo.instantiateInvocation(_invocationMirrorConstructor,
         receiver, methodName, callArguments, -1, isSuperInvocation);
   }
 
   /// Check that a call to the targetFunction is legal given the arguments.
   ///
   /// I.e. check that the number of positional parameters and the names of the
@@ skipping 39 matching lines @@
           return null;
         }
       }
 
       throw new Exception(
           'Could not find a generative constructor named "${constructor.name}" '
           'in lookup class "${lookupClass.name}"!');
     }
   }
 }