Use LibraryIndex in CoreTypes instead of extending it.

pkg/kernel/lib/transformations/method_call.dart

 // Copyright (c) 2017, 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.method_call;
 
 import 'dart:math' as math;
 
 import '../ast.dart';
 import '../class_hierarchy.dart';
@@ skipping 872 matching lines @@
     // Mark the new procedure as visited already (i.e. don't rewrite it again!)
     _visited.add(procedure);
 
     return procedure;
   }
 
   /// Creates an "new _InvocationMirror(...)" invocation.
   ConstructorInvocation _createInvocation(
       String methodName, Arguments callArguments) {
     if (_invocationMirrorConstructor == null) {
-      Class clazz = coreTypes.getClass('dart:core', '_InvocationMirror');
+      Class clazz = coreTypes.invocationMirrorClass;
       _invocationMirrorConstructor = clazz.constructors[0];
     }
 
     // The _InvocationMirror constructor takes the following arguments:
     // * Method name (a string).
     // * An arguments descriptor - a list consisting of:
     //   - number of arguments (including receiver).
     //   - number of positional arguments (including receiver).
     //   - pairs (2 entries in the list) of
     //     * named arguments name.
@@ skipping 23 matching lines @@
         new Arguments([
           new StringLiteral(methodName),
           _fixedLengthList(argumentsDescriptor),
           _fixedLengthList(arguments),
           new BoolLiteral(false)
         ]));
   }
 
   /// Create a fixed length list containing given expressions.
   Expression _fixedLengthList(List<Expression> list) {
-    _listFrom ??= coreTypes.getMember('dart:core', 'List', 'from');
+    _listFrom ??= coreTypes.listFromConstructor;
     return new StaticInvocation(
         _listFrom,
         new Arguments([new ListLiteral(list)],
             named: [new NamedExpression("growable", new BoolLiteral(false))],
             types: [const DynamicType()]));
   }
 
   /// Creates a new procedure taking given arguments, caching it.
   ///
   /// Copies any non-given default values for parameters into the new procedure
@@ skipping 358 matching lines @@
     return printStackTrace;
   }
 }
 
 class _Pair<K, V> {
   final K key;
   final V value;
 
   _Pair(this.key, this.value);
 }