Do not eagerly add guarded leaf classes with CHA; do not add them for private names.

runtime/vm/cha_test.cc

Index: runtime/vm/cha_test.cc
diff --git a/runtime/vm/cha_test.cc b/runtime/vm/cha_test.cc
index 3926daa62bc508ac3a43799c15b6fe5943668104..1cd95dc4e306ab9920c2135e55cabf7103618616 100644
--- a/runtime/vm/cha_test.cc
+++ b/runtime/vm/cha_test.cc
@@ -89,7 +89,9 @@ TEST_CASE(ClassHierarchyAnalysis) {
   EXPECT(cha.HasSubclasses(class_a));
   EXPECT(cha.HasSubclasses(class_b));
   EXPECT(!cha.HasSubclasses(class_c));
+  cha.AddToLeafClasses(class_c);
   EXPECT(!cha.HasSubclasses(class_d));
+  cha.AddToLeafClasses(class_d);
 
   EXPECT(!ContainsCid(cha.leaf_classes(), class_a.id()));
   EXPECT(!ContainsCid(cha.leaf_classes(), class_b.id()));