Add proper API for creating private symbols wrt a library.

tests/lib/lib.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.
 
 [ $compiler == dart2js && $runtime == drt ]
 convert/chunked_conversion_utf87_test: Pass, Fail # v8 bug: Issue 12293
 typed_data/byte_data_test: Pass, Fail # v8 bug: Issue 12293
 
 [ $compiler == dart2js ]
 math/double_pow_test: RuntimeError
@@ skipping 25 matching lines @@
 mirrors/typevariable_mirror_metadata_test: CompileTimeError # Issue 10905
 mirrors/unnamed_library_test: RuntimeError # Issue 10580
 async/run_async3_test: RuntimeError # _enqueueImmediate runs after Timer. http://dartbug.com/9002
 async/run_async4_test: Pass, RuntimeError # no global exception handler in isolates. http://dartbug.com/9012
 async/run_async6_test: RuntimeError # global error handling is not supported. http://dartbug.com/5958
 async/stream_controller_async_test: RuntimeError, Pass # http://dartbug.com/11953
 mirrors/typedef_test/none: RuntimeError # http://dartbug.com/6490
 mirrors/redirecting_factory_test/none: RuntimeError # Issue 6490
 mirrors/redirecting_factory_test/02: RuntimeError # Issue 6490
 mirrors/closures_test/none: RuntimeError # Issue 6490
+mirrors/symbol_validation_test: RuntimeError # Issue 13597
+mirrors/private_symbol_test: CompileTimeError # Issue 13597
+
 
 [ $runtime == safari ]
 mirrors/return_type_test: Pass, Timeout # Issue 12858
 
 [ $compiler == dart2js && $runtime != jsshell && $runtime != safari && $runtime != ff && $runtime != ie9 && $runtime != ie10]
 math/math_test: RuntimeError
 math/math2_test: RuntimeError
 
 [ $compiler == dart2js && $jscl ]
 async/future_test: RuntimeError # Timer interface not supported; dartbug.com/7728.
@@ skipping 73 matching lines @@
 
 [ $runtime == vm || ($compiler == none && $runtime == drt) ]
 async/run_async3_test: Fail # _enqueueImmediate runs after Timer. http://dartbug.com/9001.
 mirrors/hierarchy_test: Fail # TODO(ahe): This test is slightly broken. http://dartbug.com/12464
 mirrors/mixin_test/01: Fail, OK # TODO(ahe): Slight broken test to ensure test coverage on dart2js.
 mirrors/typedef_test/01: Fail, OK # Incorrect dart2js behavior.
 mirrors/redirecting_factory_test/none: Fail # Issue 13365
 mirrors/redirecting_factory_test/01: Fail # Issue 13365
 mirrors/redirecting_factory_test/02: Fail # Issue 13365
 mirrors/closures_test/01: Fail, OK # Incorrect dart2js behavior.
+mirrors/symbol_validation_test: RuntimeError # Issue 13596
 
 [ $compiler == none && $runtime == drt ]
 async/timer_isolate_test: Skip # See Issue 4997
 async/timer_not_available_test: Skip # only meant to test when there is no way to
                                      # implement timer (currently only in d8)
 mirrors/library_uri_io_test: Skip # Not intended for drt as it uses dart:io.
 mirrors/local_isolate_test: Skip # http://dartbug.com/12188
 async/run_async6_test: Fail # Issue 10910
 
 [ $compiler == none && $runtime == drt && $system == windows ]
@@ skipping 27 matching lines @@
 mirrors/generics_test/none: Fail # Issue 13432
 
 mirrors/parameter_metadata_test: Fail # Issue 13510
 mirrors/method_mirror_returntype_test: Fail # Issue 13510
 mirrors/function_type_mirror_test: Fail # Issue 13510
 mirrors/typevariable_mirror_metadata_test: Fail # Issue 13510
 
 [ $arch == x64 && $compiler == none && $runtime == vm ]
 math/double_pow_test: Pass, Fail # Issue 13543