Make TypedefMirror a direct descendant of TypeMirror.

tests/lib/lib.status

Index: tests/lib/lib.status
diff --git a/tests/lib/lib.status b/tests/lib/lib.status
index 1e442d263ecbb3d17294b6026ac3bed64f3c2e30..e9114ee081411adc026a16410bc30d32c5fe0fa1 100644
--- a/tests/lib/lib.status
+++ b/tests/lib/lib.status
@@ -144,6 +144,7 @@ mirrors/hierarchy_test: Fail # TODO(ahe): This test is slightly broken. http://d
 mirrors/mixin_test/01: Fail, OK # TODO(ahe): Slight broken test to ensure test coverage on dart2js.
 mirrors/typedef_test/01: Fail, OK # Incorrect dart2js behavior.
 mirrors/closures_test/01: Fail, OK # Incorrect dart2js behavior.
+mirrors/typevariable_mirror_metadata_test/none: RuntimeError # Issue 12282
 
 [ $compiler == none && $runtime == drt ]
 async/timer_isolate_test: Skip # See Issue 4997
@@ -179,7 +180,7 @@ mirrors/invoke_named_test/none: Fail # http://dartbug.com/13612
 mirrors/parameter_metadata_test: Fail # Issue 13510
 mirrors/method_mirror_returntype_test: Fail # Issue 13510
 mirrors/function_type_mirror_test: Fail # Issue 13510
-mirrors/typevariable_mirror_metadata_test: Fail # Issue 13510
+mirrors/typevariable_mirror_metadata_test/none: Fail # Issue 13510
 
 [ $compiler == dart2analyzer ]
 mirrors/typedef_test/none: Fail # Issue 13093
@@ -189,7 +190,7 @@ mirrors/invoke_named_test/none: Fail # http://dartbug.com/13612
 mirrors/parameter_metadata_test: Fail # Issue 13510
 mirrors/method_mirror_returntype_test: Fail # Issue 13510
 mirrors/function_type_mirror_test: Fail # Issue 13510
-mirrors/typevariable_mirror_metadata_test: Fail # Issue 13510
+mirrors/typevariable_mirror_metadata_test/none: Fail # Issue 13510
 
 [ $compiler == none && $runtime == dartium ]
 async/run_async3_test: Fail # Issue 13719: Please triage this failure.