Support covariant keyword in the VM parser

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.
 
 # These test entries will be valid for vm/dartium (with and without kernel).
 [ $compiler == none || $compiler == app_jit || $compiler == dartk || $runtime == dart_precompiled ]
 async_star_cancel_while_paused_test: RuntimeError
@@ skipping 35 matching lines @@
 enum_test: RuntimeError # Issue 28341
 
 dynamic_prefix_core_test/01: RuntimeError # Issue 12478
 multiline_strings_test: Fail # Issue 23020
 
 deferred_redirecting_factory_test: Fail # Issue 23408
 redirecting_constructor_initializer_test: RuntimeError # Issue 23488
 
 async_star_regression_2238_test: CompileTimeError, RuntimeError # drt only runtime-errs.
 
-# Doesn't yet implement `covariant` keyword.
-covariant_test/06: Fail # Issue 28166
-covariant_test/06b: Fail # Issue 28166
-covariant_test/07: Fail # Issue 28166
-covariant_test/08: Fail # Issue 28166
-covariant_test/11: Fail # Issue 28166
-covariant_test/15: Fail # Issue 28166
-covariant_test/26: Fail # Issue 28166
-covariant_test/26b: Fail # Issue 28166
-covariant_test/27: Fail # Issue 28166
-covariant_test/28: Fail # Issue 28166
-covariant_test/31: Fail # Issue 28166
-covariant_test/35: Fail # Issue 28166
-covariant_test/40: Fail # Issue 28166
-covariant_test/40b: Fail # Issue 28166
-covariant_test/42: Fail # Issue 28166
-covariant_test/46: Fail # Issue 28166
-covariant_test/46b: Fail # Issue 28166
-covariant_test/47: Fail # Issue 28166
-covariant_test/51: Fail # Issue 28166
-covariant_test/52: Fail # Issue 28166
-covariant_test/54: Fail # Issue 28166
-covariant_test/55: Fail # Issue 28166
-covariant_test/56: Fail # Issue 28166
-covariant_override_test: Fail # Issue 28166
-
-[ $compiler == none && ($runtime == dartium || $runtime == drt) && $checked ]
-covariant_test/06: Pass # Fails at runtime instead of at compile time
-covariant_test/06b: Pass # Fails at runtime instead of at compile time
-covariant_test/07: Pass # Fails at runtime instead of at compile time
-covariant_test/08: Pass # Fails at runtime instead of at compile time
-covariant_test/11: Pass # Fails at runtime instead of at compile time
-covariant_test/15: Pass # Fails at runtime instead of at compile time
-covariant_test/26: Pass # Fails at runtime instead of at compile time
-covariant_test/26b: Pass # Fails at runtime instead of at compile time
-covariant_test/27: Pass # Fails at runtime instead of at compile time
-covariant_test/28: Pass # Fails at runtime instead of at compile time
-covariant_test/31: Pass # Fails at runtime instead of at compile time
-covariant_test/35: Pass # Fails at runtime instead of at compile time
-covariant_test/46: Pass # Fails at runtime instead of at compile time
-covariant_test/46b: Pass # Fails at runtime instead of at compile time
-covariant_test/47: Pass # Fails at runtime instead of at compile time
-covariant_test/51: Pass # Fails at runtime instead of at compile time
-covariant_test/55: Pass # Fails at runtime instead of at compile time
-
 [ ($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
 
-covariant_test/48: Fail # Issue 28166
-
 [ ($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.
 
 [ ($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 236 matching lines @@
 vm/optimized_stacktrace_test: Pass, Crash # Issue 28276
 
 [$compiler == dart2analyzer]
 vm/regress_27201_test: SkipByDesign # Loads bad library, so will always crash.
 config_import_corelib_test: StaticWarning, OK
 
 null_bottom_test/none: StaticWarning, CompileTimeError # Issue 28025
 null_bottom_test/01: Pass, CompileTimeError # Issue 28025
 null_bottom_test/02: Pass, CompileTimeError # Issue 28025
 null_bottom_test/03: Pass, CompileTimeError # Issue 28025