Update MapTest to reflect SplayTree rename to SplayTreeMap.

tests/corelib/src/MapTest.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.
 
 #library("MapTest.dart");
 #import("dart:coreimpl");
 
 class MapTest {
 
   static testMain() {
     test(new HashMap());
     test(new LinkedHashMap());
-    test(new SplayTree());
+    test(new SplayTreeMap());
     testLinkedHashMap();
     testMapLiteral();
     testNullValue();
   }
 
   static void test(Map map) {
     testDeletedElement(map);
     testMap(map, 1, 2, 3, 4, 5, 6, 7, 8);
     map.clear();
     testMap(map, "value1", "value2", "value3", "value4", "value5",
@@ skipping 217 matching lines @@
     m.remove("a");
     Expect.equals(2, m.length);
     Expect.equals(null, m["a"]);
     Expect.equals(false, m.containsKey("a"));
   }
 }
 
 main() {
   MapTest.testMain();
 }