Add proper API for creating private symbols wrt a library.

pkg/pkg.status

 # 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.
 
 # Don't run any test-like files that show up in packages directories. It
 # shouldn't be necessary to run "pub install" in these packages, but if you do
 # it shouldn't break the tests.
 */packages/*/*: Skip
 */*/packages/*/*: Skip
 */*/*/packages/*/*: Skip
@@ skipping 188 matching lines @@
 [ $arch == mips ]
 *: Skip
 
 [ $arch == simmips ]
 *: Skip
 
 # Skip serialization test that explicitly has no library declaration in the
 # test on Dartium, which requires all tests to have a library.
 [ $compiler == none && ( $runtime == dartium || $runtime == drt ) ]
 serialization/test/no_library_test: Skip # Expected Failure
+serialization/test/serialization_test: Fail # Issue 13598
 
 # Skip tests on the VM if the package depends on dart:html
 [ $runtime == vm ]
 custom_element: Skip
 mdv: Skip
 mutation_observer: Skip
 polymer_expressions/test/syntax_test: Skip
 third_party/html5lib/test/browser/browser_test: Skip
+serialization/test/serialization_test: Fail # Issue 13598
 
 [ $runtime == safari || $runtime == chrome || $runtime == ie9 || $runtime == ff || $runtime == dartium || $runtime == drt ]
 docgen/test/single_library_test: Skip # Uses dart:io
 scheduled_test/test/scheduled_server_test: Skip # Uses dart:io
 
 [ $browser || $runtime == vm ]
 unittest/test/missing_tick_test: Fail, OK # This test should fail, not time out.
 
 # Issue http://dartbug.com/12930
 [ $runtime == vm ]
 intl/test/message_extraction/message_extraction_test: Pass, Fail # Issue 12930
 
 [ $compiler == none && $runtime == vm ]
 observe/test/observe_test: Pass, Fail # Issue 13543
 
 [ $compiler == none && $runtime == vm && $checked ]
 intl/test/message_extraction/failed_extraction_test: Pass, Fail # Issue 13543