Support covariant keyword in the VM parser

tests/language/language.status

Index: tests/language/language.status
diff --git a/tests/language/language.status b/tests/language/language.status
index 8438cec110b18af8df72b423785c23cc4f184a8c..43a4740037a040a0d0ef77aed8627b50d8b247fa 100644
--- a/tests/language/language.status
+++ b/tests/language/language.status
@@ -53,51 +53,6 @@ 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.
@@ -108,8 +63,6 @@ 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