Deprecate Math object in corelib in favor of dart:math library.

samples/isolate_html/isolate_sample.dart

-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// 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.
 
 #library('isolate_sample');
 
 #import('dart:html');
 #import('dart:isolate');
+#import('dart:math', prefix: 'Math');
 
 #source('IsolateSample.dart');
 
 main() {
   IsolateSample.main();
 }