Ignore deleted handles when processing weak roots.

runtime/vm/dart_api_impl_test.cc

 // Copyright (c) 2012, 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 "platform/assert.h"
 #include "platform/utils.h"
 #include "vm/class_finalizer.h"
 #include "vm/dart_api_impl.h"
 #include "vm/dart_api_state.h"
@@ skipping 1319 matching lines @@
   Isolate::Current()->heap()->CollectGarbage(Heap::kOld);
 
   // weak ref to old space object should now be cleared
   EXPECT_VALID(weak_new_ref);
   EXPECT(Dart_IsNull(weak_new_ref));
   EXPECT_VALID(weak_old_ref);
   EXPECT(Dart_IsNull(weak_old_ref));
 
   Dart_DeletePersistentHandle(weak_new_ref);
   Dart_DeletePersistentHandle(weak_old_ref);
+
+  // garbage collect one last time to revisit deleted handles
+  Isolate::Current()->heap()->CollectGarbage(Heap::kNew);
+  Isolate::Current()->heap()->CollectGarbage(Heap::kOld);
 }
 
 
 static void WeakPersistentHandlePeerFinalizer(Dart_Handle handle, void* peer) {
   *static_cast<int*>(peer) = 42;
 }
 
 
 TEST_CASE(WeakPersistentHandleCallback) {
   Dart_Handle weak_ref = Dart_Null();
@@ skipping 2377 matching lines @@
   // We should have received the expected number of interrupts.
   EXPECT_EQ(kInterruptCount, interrupt_count);
 
   // Give the spawned thread enough time to properly exit.
   Isolate::SetInterruptCallback(saved);
 }
 
 #endif  // defined(TARGET_ARCH_IA32) || defined(TARGET_ARCH_X64).
 
 }  // namespace dart