Move Null type to the Bottom in the VM (fixes #28025).

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.
 
-[ $compiler == none || $compiler == app_jit ]
-null_is_bottom_test/22: RuntimeError # Issue 28025
-null_is_bottom_test/34: RuntimeError # Issue 28025
-
 [ $compiler == none || $compiler == precompiler || $compiler == app_jit ]
 # Other issues:
 generic_methods_type_expression_test: RuntimeError # Issue 25869
-null_is_bottom_test/05: RuntimeError # Issue 28025
-null_is_bottom_test/07: RuntimeError # Issue 28025
-null_is_bottom_test/20: RuntimeError # Issue 28025
-null_is_bottom_test/25: RuntimeError # Issue 28025
-null_is_bottom_test/27: RuntimeError # Issue 28025
-null_is_bottom_test/32: RuntimeError # Issue 28025
-null_is_bottom_test/37: RuntimeError # Issue 28025
-null_is_bottom_test/39: RuntimeError # Issue 28025
 
 # This is OK for now, but we may want to change the semantics to match the test.
 async_star_pause_test: Fail, OK
 
 # These tests are skipped in the VM because it has "--supermixin"
 # functionality enabled unconditionally.  The tests should be removed
 # once the same is true for analyzer (#24478) and dart2js (#23773)
 mixin_illegal_super_use_test: Skip # Issues 24478 and 23773
 mixin_illegal_superclass_test: Skip # Issues 24478 and 23773
 
@@ skipping 32 matching lines @@
 
 [ ($compiler == none || $compiler == precompiler || $compiler == app_jit) && $checked ]
 # These generic functions tests pass for the wrong reason in checked mode,
 # because the parsed type parameters are mapped to dynamic type.
 generic_methods_function_type_test: Pass # Issue 25869
 generic_methods_test: Pass # Issue 25869
 generic_methods_new_test: Pass # Issue 25869
 generic_local_functions_test: Pass # Issue 25869
 generic_functions_test: Pass # Issue 25869
 generic_methods_generic_function_parameter_test: Pass # Issue 25869
-null_is_bottom_test/03: RuntimeError # Issue 28025
-null_is_bottom_test/18: RuntimeError # Issue 28025
-null_is_bottom_test/23: RuntimeError # Issue 28025
-null_is_bottom_test/30: RuntimeError # Issue 28025
-null_is_bottom_test/35: RuntimeError # Issue 28025
 
 [ ($compiler == none || $compiler == precompiler || $compiler == app_jit) && ($runtime == vm || $runtime == dart_precompiled) ]
-
 class_keyword_test/02: MissingCompileTimeError # Issue 13627
 unicode_bom_test: Fail # Issue 16067
 vm/debug_break_enabled_vm_test/01: Crash, OK # Expected to hit breakpoint.
 try_catch_optimized1_test: Skip # Srdjan investigating
 
 [ ($compiler == none || $compiler == precompiler || $compiler == app_jit) && $checked ]
 type_variable_bounds4_test/01: Fail # Issue 14006
 
 [ ($compiler == none || $compiler == precompiler || $compiler == app_jit) && (($runtime == vm || $runtime == dart_precompiled) || $runtime == drt || $runtime == dartium) ]
 dynamic_prefix_core_test/none: Fail # Issue 12478
@@ skipping 251 matching lines @@
 null_bottom_test/01: Pass, CompileTimeError # Issue 28025
 null_bottom_test/02: Pass, CompileTimeError # Issue 28025
 null_bottom_test/03: Pass, CompileTimeError # Issue 28025
 
 # Issue #28236
 async_await_test: StaticWarning
 async_star_pause_test: StaticWarning
 async_star_test: StaticWarning
 regress_18535_test: StaticWarning
 
-[ $runtime == dart_precompiled || $runtime == vm || $runtime == dartium]
-null_bottom_test/none: RuntimeError # Issue 28025
-null_bottom_test/01: RuntimeError # Issue 28025
-null_bottom_test/02: RuntimeError # Issue 28025