Add Null class to dart:core.

tests/language/language.status

Index: tests/language/language.status
diff --git a/tests/language/language.status b/tests/language/language.status
index 41e5205a3361f660d2e980bb8ad39d1d7426361d..62ee8a11afd558b93671a950fc6a8bc41b875639 100644
--- a/tests/language/language.status
+++ b/tests/language/language.status
@@ -302,3 +302,30 @@ 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.