Use more entities in program_builder, collector and registry

pkg/compiler/lib/src/js_emitter/sorter.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 dart2js.js_emitter.sorter;
+
+import '../elements/elements.dart';
+import '../elements/entities.dart';
+
+/// Sorting strategy for libraries, classes and members.
+abstract class Sorter {
+  /// Returns a sorted list of [libraries].
+  Iterable<LibraryEntity> sortLibraries(Iterable<LibraryEntity> libraries);
+
+  /// Returns a sorted list of [classes].
+  Iterable<ClassEntity> sortClasses(Iterable<ClassEntity> classes);
+
+  /// Returns a sorted list of [members].
+  Iterable<MemberEntity> sortMembers(Iterable<MemberEntity> members);
+}
+
+class ElementSorter implements Sorter {
+  const ElementSorter();
+
+  @override
+  List<LibraryEntity> sortLibraries(Iterable<LibraryEntity> libraries) {
+    return Elements.sortedByPosition(new List.from(libraries, growable: false));
+  }
+
+  @override
+  List<ClassEntity> sortClasses(Iterable<ClassEntity> classes) {
+    return Elements.sortedByPosition(new List.from(classes, growable: false));
+  }
+
+  @override
+  List<MemberEntity> sortMembers(Iterable<MemberEntity> members) {
+    return Elements.sortedByPosition(new List.from(members, growable: false));
+  }
+}