Add Null class to dart:core.

tests/language/language.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.
 
 # This directory contains tests that are intended to show the
 # current state of the language.
 
 # In order to maintain maximum test coverage for all builds,
 # please use the following procedure to mark a test
 # failed on architectures other than the one you are working on.
@@ skipping 284 matching lines @@
 [ $compiler == dart2dart && $minified ]
 super_getter_setter_test: Fail # Issue 11065.
 
 # TODO(tball): Assign proper bug numbers.
 class_literal_test: Fail
 
 import_core_prefix_test: Pass
 prefix22_test: Pass
 invocation_mirror_test: Fail, OK # hardcoded names.
 super_call4_test: Fail, OK # hardcoded names.
+
+[ $arch == simarm || $arch == arm ]
+# TODO(zra): Check to see if the ASSERT that fails in debug mode is correct
+stack_overflow_test: Crash, Pass # Passes in release mode.
+stack_overflow_stacktrace_test: Crash, Pass # Passes in release mode.
+try_catch4_test: Crash, Fail
+
+[ $arch == arm && $mode == release ]
+arithmetic_test: Fail
+
+[ $arch == mips ]
+*: Skip
+
+
+[ $arch == simmips ]
+arithmetic_test: Crash  # Too far relative branch.
+large_implicit_getter_test: Crash  # Too far relative branch.
+# TODO(zra): Check to see if the ASSERT that fails in debug mode is correct
+stack_overflow_test: Crash, Pass # Passes in release mode.
+stack_overflow_stacktrace_test: Crash, Pass # Passes in release mode.
+try_catch4_test: Fail
+
+[ $runtime == vm ]
+null_test/none: Fail  # Issue 12382.
+
+[ $compiler == dart2js ]
+#null_test/none: Fail  # Doesn't handle "x is Null" correctly.