fix #30423, covariant parameter tearoff type should be Object

tests/language_strong/function_subtype2_test.dart

Index: tests/language_strong/function_subtype2_test.dart
diff --git a/tests/language_strong/function_subtype2_test.dart b/tests/language_strong/function_subtype2_test.dart
index 01a15f1cee14c3c5a78ca15be42a90b2814520cc..0f92421d0750e8e6fce8553265533593eba8aa71 100644
--- a/tests/language_strong/function_subtype2_test.dart
+++ b/tests/language_strong/function_subtype2_test.dart
@@ -14,11 +14,11 @@ typedef void T4(int a, [int b, int c]);
 typedef void T5([int a, int b, int c]);
 
 class C<T, S, U> {
-  void m1(T a, S b) {}
-  void m2(T a, [S b]) {}
-  void m3([T a, S b]) {}
-  void m4(T a, [S b, U c]) {}
-  void m5([T a, S b, U c]) {}
+  get m1 => (T a, S b) {};

[Jennifer Messerly, 2017/08/12 00:10:49]

FYI: this test intent seems to be testing general function subtyping, not class
generics specifically, so I updated the test to preserve the old behavior.

+  get m2 => (T a, [S b]) {};
+  get m3 => ([T a, S b]) {};
+  get m4 => (T a, [S b, U c]) {};
+  get m5 => ([T a, S b, U c]) {};
 }
 
 main() {