Use Uint32List as the return type of _IntervalListBuilder.buildIntervalList().

pkg/kernel/lib/class_hierarchy.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 file.
 library kernel.class_hierarchy;
 
 import 'ast.dart';
 import 'dart:math';
 import 'dart:typed_data';
 import 'src/heap.dart';
 import 'type_algebra.dart';
@@ skipping 805 matching lines @@
   void addSingleton(int x) {
     addInterval(x, x + 1);
   }
 
   void addIntervalList(Uint32List intervals) {
     for (int i = 0; i < intervals.length; i += 2) {
       addInterval(intervals[i], intervals[i + 1]);
     }
   }
 
-  List<int> buildIntervalList() {
+  Uint32List buildIntervalList() {
     // Sort the event points and sweep left to right while tracking how many
     // intervals we are currently inside.  Record an interval end point when the
     // number of intervals drop to zero or increase from zero to one.
     // Event points are encoded so that an opening end point occur before a
     // closing end point at the same value.
     events.sort();
     int insideCount = 0; // The number of intervals we are currently inside.
     int storeIndex = 0;
     for (int i = 0; i < events.length; ++i) {
       int event = events[i];
@@ skipping 232 matching lines @@
 class _LubHeap extends Heap<_ClassInfo> {
   @override
   bool sortsBefore(_ClassInfo a, _ClassInfo b) => sortsBeforeStatic(a, b);
 
   static bool sortsBeforeStatic(_ClassInfo a, _ClassInfo b) {
     if (a.depth > b.depth) return true;
     if (a.depth < b.depth) return false;
     return a.topologicalIndex < b.topologicalIndex;
   }
 }