Use LibraryIndex in CoreTypes instead of extending it.

pkg/kernel/lib/transformations/method_call.dart

Index: pkg/kernel/lib/transformations/method_call.dart
diff --git a/pkg/kernel/lib/transformations/method_call.dart b/pkg/kernel/lib/transformations/method_call.dart
index 7dabcbce168c45f0f1230dbc9a9a20565e434897..26ee679af01fb4aa45cf47c15093dc1fc953134f 100644
--- a/pkg/kernel/lib/transformations/method_call.dart
+++ b/pkg/kernel/lib/transformations/method_call.dart
@@ -890,7 +890,7 @@ class MethodCallTransformer extends Transformer {
   ConstructorInvocation _createInvocation(
       String methodName, Arguments callArguments) {
     if (_invocationMirrorConstructor == null) {
-      Class clazz = coreTypes.getClass('dart:core', '_InvocationMirror');
+      Class clazz = coreTypes.invocationMirrorClass;
       _invocationMirrorConstructor = clazz.constructors[0];
     }
 
@@ -934,7 +934,7 @@ class MethodCallTransformer extends Transformer {
 
   /// 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)],