pkg/compiler: fix imports

pkg/compiler/lib/src/resolution/semantic_visitor.dart

 // Copyright (c) 2015, 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.semantics_visitor;
 
 import '../common.dart';
 import '../constants/expressions.dart';
 import '../dart_types.dart';
+import '../elements/elements.dart';
 import '../tree/tree.dart';
-import '../elements/elements.dart';
 import '../universe/call_structure.dart' show CallStructure;
 import '../universe/selector.dart' show Selector;
-
 import 'operators.dart';
 import 'send_resolver.dart';
 import 'send_structure.dart';
 import 'tree_elements.dart';
 
 part 'semantic_visitor_mixins.dart';
 
 /// Mixin that couples a [SendResolverMixin] to a [SemanticSendVisitor] in a
 /// [Visitor].
 abstract class SemanticSendResolvedMixin<R, A> implements Visitor<R> {
@@ skipping 4682 matching lines @@
   ///
   /// For instance `this._(42)` in:
   ///
   ///     class C {
   ///       C() : this._(42);
   ///     }
   ///
   R errorUnresolvedThisConstructorInvoke(
       Send node, Element element, NodeList arguments, Selector selector, A arg);
 }