Change Set.add to return a boolean indicating success.

tests/corelib/set_test.dart

 // Copyright (c) 2011, 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.
 
 class SetTest {
 
   static testMain() {
     Set set = new Set();
     Expect.equals(0, set.length);
-    set.add(1);
+    Expect.equals(true, set.add(1));
     Expect.equals(1, set.length);
     Expect.equals(true, set.contains(1));
 
-    set.add(1);
+    Expect.equals(false, set.add(1));
     Expect.equals(1, set.length);
     Expect.equals(true, set.contains(1));
 
-    set.remove(1);
+    Expect.equals(true, set.remove(1));
     Expect.equals(0, set.length);
     Expect.equals(false, set.contains(1));
 
     for (int i = 0; i < 10; i++) {
-      set.add(i);
+      Expect.equals(true, set.add(i));
     }
 
     Expect.equals(10, set.length);
     for (int i = 0; i < 10; i++) {
       Expect.equals(true, set.contains(i));
     }
 
     Expect.equals(10, set.length);
 
     for (int i = 10; i < 20; i++) {
@@ skipping 73 matching lines @@
     filtered.add(10);
     Expect.equals(false, filtered.every(testEvery));
 
     // Test Set.some.
     testSome(int val) {
       return (val == 4);
     }
 
     Expect.equals(true, set.some(testSome));
     Expect.equals(true, filtered.some(testSome));
-    filtered.remove(4);
+    Expect.equals(true, filtered.remove(4));
     Expect.equals(false, filtered.some(testSome));
 
     // Test Set.intersection.
     Set intersection = set.intersection(filtered);
     Expect.equals(true, set.contains(0));
     Expect.equals(true, set.contains(2));
     Expect.equals(true, set.contains(6));
     Expect.equals(true, set.contains(8));
     Expect.equals(false, intersection.contains(1));
     Expect.equals(false, intersection.contains(3));
@@ skipping 26 matching lines @@
     for (int i = 0; i < 10; i++) {
       Expect.equals(true, set.contains(i));
     }
     for (int i = 10; i < 20; i++) {
       Expect.equals(false, set.contains(i));
     }
 
     // Test Set.clear.
     set.clear();
     Expect.equals(0, set.length);
-    set.add(11);
+    Expect.equals(true, set.add(11));
     Expect.equals(1, set.length);
   }
 }
 
 main() {
   SetTest.testMain();
 }