Add magnitude getter to Point.

tests/html/point_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.
 
 library point_test;
 
 import 'dart:html';
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_config.dart';
 
@@ skipping 94 matching lines @@
   });
 
   test('hashCode', () {
     var a = new Point(0, 1);
     var b = new Point(0, 1);
     expect(a.hashCode, b.hashCode);
 
     var c = new Point(1, 0);
     expect(a.hashCode == c.hashCode, isFalse);
   });
+
+  test('magnitute', () {
+    var a = new Point(5, 10);
+    var b = new Point(0, 0);
+    expect(a.magnitude, a.distanceTo(b));
+    expect(b.magnitude, 0);
+
+    var c = new Point(-5, -10);
+    expect(c.magnitude, a.distanceTo(b));
+  });
 }