Move dart_types to elements/resolution_types

pkg/compiler/lib/src/kernel/unresolved.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.md file.
 
 import 'package:kernel/ast.dart' as ir;
 
-import "../dart_types.dart" show DartType, InterfaceType;
+import "../elements/resolution_types.dart" show DartType, InterfaceType;
 import "../elements/elements.dart"
     show
         AstElement,
         ConstructorElement,
         Element,
         ErroneousElement,
         FunctionElement,
         MethodElement;
 import "../resolution/operators.dart"
     show AssignmentOperator, BinaryOperator, IncDecOperator, UnaryOperator;
@@ skipping 548 matching lines @@
     return buildUnresolvedSuperIndexAccessor(index, element)
         .buildNullAwareAssignment(visitForValue(rhs), null);
   }
 
   ir.Expression visitUnresolvedSuperSet(
       Send node, Element element, Node rhs, _) {
     return buildThrowUnresolvedSuperSetter(
         '${node.selector}', visitForValue(rhs));
   }
 }