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

runtime/vm/dart_api_impl.h

Index: runtime/vm/dart_api_impl.h
diff --git a/runtime/vm/dart_api_impl.h b/runtime/vm/dart_api_impl.h
index f597ca29d4e782aec56cab3c99d5d6b0654985c4..d61a3f8c55a9b0df91d7da90f582415161ee589e 100644
--- a/runtime/vm/dart_api_impl.h
+++ b/runtime/vm/dart_api_impl.h
@@ -9,6 +9,7 @@
 #include "vm/native_arguments.h"
 #include "vm/object.h"
 #include "vm/safepoint.h"
+#include "vm/thread_registry.h"
 
 namespace dart {
 
@@ -18,6 +19,7 @@ class FinalizablePersistentHandle;
 class LocalHandle;
 class PersistentHandle;
 class ReusableObjectHandleScope;
+class ThreadRegistry;
 
 const char* CanonicalFunction(const char* func);
 
@@ -166,6 +168,9 @@ class Api : AllStatic {
     return (ClassId(handle) >= kInstanceCid);
   }
 
+  // Returns true if the handle is non-dangling.
+  static bool IsValid(Dart_Handle handle);
+
   // Returns true if the handle holds an Error.
   static bool IsError(Dart_Handle handle) {
     return RawObject::IsErrorClassId(ClassId(handle));