Resolution for issue #5092: Unit test handle checks consider dangling handles to be valid.

runtime/vm/dart_api_impl.cc

Index: runtime/vm/dart_api_impl.cc
diff --git a/runtime/vm/dart_api_impl.cc b/runtime/vm/dart_api_impl.cc
index 22e23911615cecd9d72dcd545b018d2983ff3b1b..4a0d57933bfc5dadea42c7cacdd77dbb5afbaea2 100644
--- a/runtime/vm/dart_api_impl.cc
+++ b/runtime/vm/dart_api_impl.cc
@@ -759,6 +759,11 @@ void FinalizablePersistentHandle::Finalize(
 
 // --- Handles ---
 
+DART_EXPORT bool Dart_IsValid(Dart_Handle handle) {
+  return Api::IsValid(handle);
+}
+
+
 DART_EXPORT bool Dart_IsError(Dart_Handle handle) {
   return Api::IsError(handle);
 }