Make TypedefMirror a direct descendant of TypeMirror.

tests/lib/mirrors/typevariable_mirror_metadata_test.dart

Index: tests/lib/mirrors/typevariable_mirror_metadata_test.dart
diff --git a/tests/lib/mirrors/typevariable_mirror_metadata_test.dart b/tests/lib/mirrors/typevariable_mirror_metadata_test.dart
index 4f86b6d4796005e7f7c0d09912b49663ad53ad3f..fa05d64e21d1a9e112083eec68684fe581378d91 100644
--- a/tests/lib/mirrors/typevariable_mirror_metadata_test.dart
+++ b/tests/lib/mirrors/typevariable_mirror_metadata_test.dart
@@ -27,7 +27,9 @@ main() {
   cm = reflectClass(B);
   checkMetadata(cm.typeVariables[0], [m3]);
 
-  TypedefMirror tm = reflectClass(Predicate);
-  FunctionTypeMirror ftm = tm.referent;
-  checkMetadata(ftm.typeVariables[0], [m1, m2]);
+  // Partial coverage.
+  return; /// 01: ok
+
+  TypedefMirror tm = reflectType(Predicate);
+  checkMetadata(tm.typeVariables[0], [m1, m2]);
 }