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

runtime/vm/dart_api_impl.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "include/dart_api.h"
 #include "include/dart_mirrors_api.h"
 #include "include/dart_native_api.h"
 
 #include "platform/assert.h"
 #include "lib/stacktrace.h"
@@ skipping 741 matching lines @@
   Dart_WeakPersistentHandle object = handle->apiHandle();
   (*callback)(isolate->init_callback_data(), object, peer);
   ApiState* state = isolate->api_state();
   ASSERT(state != NULL);
   state->weak_persistent_handles().FreeHandle(handle);
 }
 
 
 // --- 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);
 }
 
 
 DART_EXPORT bool Dart_IsApiError(Dart_Handle object) {
   return Api::ClassId(object) == kApiErrorCid;
 }
 
 
@@ skipping 6019 matching lines @@
 }
 
 
 DART_EXPORT void Dart_DumpNativeStackTrace(void* context) {
 #ifndef PRODUCT
   Profiler::DumpStackTrace(context);
 #endif
 }
 
 }  // namespace dart