Add MapBase and UnmodifiableMapView classes to dart:collection.

tests/corelib/integer_to_string_test.dart

 // Copyright (c) 2012, 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";
 
 main() {
   /// Test that converting [value] to a string gives [expect].
   /// Also test that `-value` gives `"-"+expect`.
   test(int value, String expect) {
     Expect.equals(expect, value.toString());
     Expect.equals(expect, "$value");
     Expect.equals(expect, (new StringBuffer()..write(value)).toString());
     if (value == 0) return;
     expect = "-$expect";
     value = -value;
     Expect.equals(expect, value.toString());
     Expect.equals(expect, "$value");
     Expect.equals(expect, (new StringBuffer()..write(value)).toString());
   }
 
-  // Null.
+  // Very simple tests.
   test(0, "0");
   test(1, "1");
   test(2, "2");
   test(5, "5");
 
   // Binary special cases.
 
   // ~2^30.
   test(0x3fffffff, "1073741823");
   test(0x40000000, "1073741824");
@@ skipping 46 matching lines @@
     number *= 10;
   }
   // Fails to represent exactly in dart2js.
   for (int i = 15; i < 22; i++) {                     /// 01: continued
     test(number - 1, "9" * i);                        /// 01: continued
     test(number, "1" + "0" * i);                      /// 01: continued
     test(number + 1, "1" + "0" * (i - 1) + "1");      /// 01: continued
     number *= 10;                                     /// 01: continued
   }                                                   /// 01: continued
 }