Add dart2snapshot compiler and dart_snapshotted runtime to test scripts

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.
 
 [ $unchecked ]
 mirrors/redirecting_factory_different_type_test: SkipByDesign # Tests type checks.
 
 [ $compiler == dart2js ]
 async/schedule_microtask6_test: RuntimeError # global error handling is not supported. Issue 5958
 
@@ skipping 170 matching lines @@
 
 [ $compiler == dart2js && ( $browser || $runtime == d8 ) ]
 async/timer_not_available_test: Fail, OK # only meant to test when there is no way to
                                          # implement timer (currently only in jsshell)
 
 # 'js' tests import the dart:js library, so they only make sense in
 # a browser environment.
 [ ($runtime == vm || $runtime == dart_precompiled) ]
 js/*: Skip
 
+# 'js' tests import the dart:js library, so they only make sense in
+# a browser environment.
+[ $runtime == dart_snapshotted ]
+js/*: SkipByDesign
+mirrors/*: SkipByDesign
+
 [ $compiler == dart2js && $minified ]
 mirrors/mirrors_used_get_name_test: RuntimeError
 mirrors/mirrors_used_get_name2_test: RuntimeError
 
 [ $runtime == ff ]
 # FF setTimeout can fire early: https://bugzilla.mozilla.org/show_bug.cgi?id=291386
 convert/streamed_conversion_utf8_decode_test: Pass, Slow  # Issue 12029
 mirrors/mirrors_reader_test: Timeout, Slow, RuntimeError # Issue 16589
 
 [ $runtime == chrome && $system == macos ]
@@ skipping 144 matching lines @@
 mirrors/mirrors_used_typedef_declaration_test/none: Crash # Assertion failure: typedef(Foo) has not been checked for cycles.
 mirrors/typedef_library_test: Crash # Assertion failure: typedef(G) has not been checked for cycles.
 
 [ $compiler != dart2js ]
 async/dart2js_uncaught_error_test: Skip  # JS-integration only test
 
 [ ($noopt || $compiler == precompiler) ]
 mirrors/*: SkipByDesign
 convert/chunked_conversion_utf88_test: Pass, Timeout
 convert/utf85_test: Pass, Timeout