Background compiler should validate CHA decisions before committing the code.

runtime/vm/flow_graph_type_propagator.cc

Index: runtime/vm/flow_graph_type_propagator.cc
diff --git a/runtime/vm/flow_graph_type_propagator.cc b/runtime/vm/flow_graph_type_propagator.cc
index af0a03fcd42e3eb46970811120a75ab8a6a9dd7d..1138c6a20c562577a773ce53cb6d3d58371f792e 100644
--- a/runtime/vm/flow_graph_type_propagator.cc
+++ b/runtime/vm/flow_graph_type_propagator.cc
@@ -504,7 +504,7 @@ intptr_t CompileType::ToNullableCid() {
                 type_class.ToCString());
           }
           if (FLAG_use_cha_deopt) {
-            cha->AddToLeafClasses(type_class);
+            cha->AddToGuardedClasses(type_class, /*subclass_count=*/0);
           }
           cid_ = type_class.id();
         } else {
@@ -752,7 +752,8 @@ CompileType ParameterInstr::ComputeType() const {
                   type_class.ToCString());
             }
             if (FLAG_use_cha_deopt) {
-              thread->cha()->AddToLeafClasses(type_class);
+              thread->cha()->AddToGuardedClasses(
+                  type_class, /*subclass_count=*/0);
             }
             cid = type_class.id();
           }