Add a much simplified set implementation designed to waste little memory for small sets.

tests/compiler/dart2js/setlet_test.dart

+// Copyright (c) 2013, 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.
+
+import "package:expect/expect.dart";
+import '../../../sdk/lib/_internal/compiler/implementation/util/setlet.dart';
+
+main() {
+  for (int i = 1; i <= 32; i++) {
+    test(i);
+  }
+}
+
+test(int size) {
+  var setlet = new Setlet();
+  for (int i = 0; i < size; i++) {
+    Expect.isTrue(setlet.isEmpty == (i == 0));
+    setlet.add(i);
+    Expect.equals(i + 1, setlet.length);
+    Expect.isFalse(setlet.isEmpty);
+    for (int j = 0; j < size + size; j++) {
+      Expect.isTrue(setlet.contains(j) == (j <= i));
+    }
+    Expect.isTrue(setlet.remove(i));
+    Expect.isFalse(setlet.remove(i + 1));
+    setlet.add(i);
+
+    List expectedElements = [];
+    for (int j = 0; j <= i; j++) expectedElements.add(j);
+
+    List actualElements = [];
+    setlet.forEach((each) => actualElements.add(each));
+    Expect.listEquals(expectedElements, actualElements);
+
+    actualElements = [];
+    for (var each in setlet) actualElements.add(each);
+    Expect.listEquals(expectedElements, actualElements);
+  }
+
+  for (int i = 0; i < size; i++) {
+    Expect.equals(size, setlet.length);
+
+    // Try removing all possible ranges one by one and re-add them.
+    for (int k = size; k > i; --k) {
+      for (int j = i; j < k; j++) {
+        Expect.isTrue(setlet.remove(j));
+        Expect.equals(size - (j - i + 1), setlet.length);
+        Expect.isFalse(setlet.remove(j));
+        Expect.isFalse(setlet.contains(j));
+      }
+
+      for (int j = i; j < k; j++) {
+        setlet.add(j);
+      }
+    }
+
+    Expect.equals(size, setlet.length);
+    Expect.isTrue(setlet.contains(i));
+  }
+}