Revert "Background finalization."

runtime/vm/thread.h

 // Copyright (c) 2015, 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.
 
 #ifndef VM_THREAD_H_
 #define VM_THREAD_H_
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/atomic.h"
@@ skipping 127 matching lines @@
 // must currently be called manually (issue 23474).
 class Thread : public BaseThread {
  public:
   // The kind of task this thread is performing. Sampled by the profiler.
   enum TaskKind {
     kUnknownTask = 0x0,
     kMutatorTask = 0x1,
     kCompilerTask = 0x2,
     kSweeperTask = 0x4,
     kMarkerTask = 0x8,
-    kFinalizerTask = 0x10,
   };
   ~Thread();
 
   // The currently executing thread, or NULL if not yet initialized.
   static Thread* Current() {
     BaseThread* thread = OSThread::GetCurrentTLS();
     if (thread == NULL || thread->is_os_thread()) {
       return NULL;
     }
     return reinterpret_cast<Thread*>(thread);
@@ skipping 607 matching lines @@
 // Disable thread interrupts.
 class DisableThreadInterruptsScope : public StackResource {
  public:
   explicit DisableThreadInterruptsScope(Thread* thread);
   ~DisableThreadInterruptsScope();
 };
 
 }  // namespace dart
 
 #endif  // VM_THREAD_H_