Normalize type masks to use the least upper instantiated subclass/type.

tests/compiler/dart2js/patch_test.dart

Index: tests/compiler/dart2js/patch_test.dart
diff --git a/tests/compiler/dart2js/patch_test.dart b/tests/compiler/dart2js/patch_test.dart
index 7c3ca3d0525fbd4a04a4f8a937697e517af40572..3429a2c06daad9f2e91299ab7d34e872749a1e04 100644
--- a/tests/compiler/dart2js/patch_test.dart
+++ b/tests/compiler/dart2js/patch_test.dart
@@ -914,6 +914,7 @@ Future testPatchAndSelector() async {
       """,
       runCompiler: true, analyzeOnly: true);
   World world = compiler.world;
+  world.populate();
 
   ClassElement cls = ensure(compiler, "A", compiler.coreLibrary.find,
                             expectIsPatched: true);