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

tests/try/poi/forget_element_test.dart

Index: tests/try/poi/forget_element_test.dart
diff --git a/tests/try/poi/forget_element_test.dart b/tests/try/poi/forget_element_test.dart
index 22b61ceba0ad65e1f7b2f77c7511ab3ec9ac3411..095b52cecb0d9c125ecc67063d83b1a771ab52d2 100644
--- a/tests/try/poi/forget_element_test.dart
+++ b/tests/try/poi/forget_element_test.dart
@@ -260,12 +260,12 @@ class ForgetElementTestCase extends CompilerTestCase {
   }
 
   Iterable codegenSeenClassesIn(LibraryElement library) {
-    return compiler.codegenWorld.allInstantiatedClasses.where(
+    return compiler.enqueuer.codegen.processedClasses.where(
         (e) => e.library == library);
   }
 
   Iterable resolutionSeenClassesIn(LibraryElement library) {
-    return compiler.resolverWorld.allInstantiatedClasses.where(
+    return compiler.enqueuer.resolution.processedClasses.where(
         (e) => e.library == library);
   }
 }