Support 'implements' clause on typedef mixin applications.

tests/language/language.status

Index: tests/language/language.status
diff --git a/tests/language/language.status b/tests/language/language.status
index 4e639808767c597b7621c9c032237e446abd1594..0707d87dad60578ab407f77a657af69f3d851be5 100644
--- a/tests/language/language.status
+++ b/tests/language/language.status
@@ -69,6 +69,7 @@ mixin_illegal_superclass_test/none: Fail
 mixin_illegal_constructor_test/none: Fail
 mixin_illegal_static_access_test: Fail
 mixin_illegal_super_use_test/none: Fail
+mixin_implements_test: Fail
 
 [ $compiler == none && ($system == macos || $system == linux) && $arch == ia32 && $checked ]
 gc_test: Skip  # Issue 1487, flaky.
@@ -362,6 +363,7 @@ mixin_illegal_syntax_test/none: Fail       # VM issue
 mixin_illegal_superclass_test/none: Fail   # VM issue
 mixin_illegal_constructor_test/none: Fail  # VM issue
 mixin_illegal_super_use_test/none: Fail    # VM issue
+mixin_implements_test: Fail                # VM issue
 
 # Malformed types not handled as unresolved:
 import_core_prefix_test: Fail