Check const map literal keys and switch case exprs using type of constant.

tests/language/const_map3_test.dart

Index: tests/language/const_map3_test.dart
diff --git a/tests/language/const_map2_test.dart b/tests/language/const_map3_test.dart
similarity index 85%
copy from tests/language/const_map2_test.dart
copy to tests/language/const_map3_test.dart
index 6b599f70d1585a34903a5c6bf1f136c9197123f4..730cb013750a403dbbb3fe17e982bc46a704b394 100644
--- a/tests/language/const_map2_test.dart
+++ b/tests/language/const_map3_test.dart
@@ -5,7 +5,7 @@
 import "package:expect/expect.dart";
 
 class A {
-  const factory A() = B;
+  static const b = const B();
 }
 
 class B implements A {
@@ -21,9 +21,9 @@ confuse(x) {
 
 main() {
   // It is a compile-time error if the key type overrides operator ==.
-  var m = const { const A(): 42 };
+  var m = const { A.b: 42 };
   Expect.equals(42, m[confuse(const B())]);
 
-  m = const { "foo": 99, const A(): 499 };
+  m = const { "foo": 99, A.b: 499 };
   Expect.equals(499, m[confuse(const B())]);
 }