Treat background finalization as another GC task so it won't run in parallel with the marker.

runtime/vm/isolate.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 "vm/isolate.h"
 
 #include "include/dart_api.h"
 #include "include/dart_native_api.h"
 #include "platform/assert.h"
 #include "platform/text_buffer.h"
@@ skipping 1718 matching lines @@
     }
   }
 
   // Remove this isolate from the list *before* we start tearing it down, to
   // avoid exposing it in a state of decay.
   RemoveIsolateFromList(this);
 
   if (heap_ != NULL) {
     // Wait for any concurrent GC tasks to finish before shutting down.
     // TODO(koda): Support faster sweeper shutdown (e.g., after current page).
-    {
-      PageSpace* old_space = heap_->old_space();
-      MonitorLocker ml(old_space->tasks_lock());
-      while (old_space->tasks() > 0) {
-        ml.Wait();
-      }
-    }
-
-    // Wait for background finalization to finish before shutting down.
-    {
-      MonitorLocker ml(heap_->finalization_tasks_lock());
-      while (heap_->finalization_tasks() > 0) {
-        ml.Wait();
-      }
+    PageSpace* old_space = heap_->old_space();
+    MonitorLocker ml(old_space->tasks_lock());
+    while (old_space->tasks() > 0) {
+      ml.Wait();
     }
   }
 
   if (FLAG_check_reloaded && is_runnable() &&
       (this != Dart::vm_isolate()) &&
       !ServiceIsolate::IsServiceIsolateDescendant(this)) {
     if (!HasAttemptedReload()) {
       FATAL("Isolate did not reload before exiting and "
             "--check-reloaded is enabled.\n");
     }
@@ skipping 1137 matching lines @@
 void IsolateSpawnState::DecrementSpawnCount() {
   ASSERT(spawn_count_monitor_ != NULL);
   ASSERT(spawn_count_ != NULL);
   MonitorLocker ml(spawn_count_monitor_);
   ASSERT(*spawn_count_ > 0);
   *spawn_count_ = *spawn_count_ - 1;
   ml.Notify();
 }
 
 }  // namespace dart