Simplify ownership of a ThreadState's interruptors.

Source/platform/WebThreadSupportingGC.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "platform/WebThreadSupportingGC.h"
 
 #include "platform/heap/SafePoint.h"
 #include "public/platform/WebScheduler.h"
 #include "wtf/Threading.h"
@@ skipping 18 matching lines @@
     if (ThreadState::current()) {
         // WebThread's destructor blocks until all the tasks are processed.
         SafePointScope scope(ThreadState::HeapPointersOnStack);
         m_thread.clear();
     }
 }
 
 void WebThreadSupportingGC::initialize()
 {
     m_pendingGCRunner = adoptPtr(new PendingGCRunner);
-    m_messageLoopInterruptor = adoptPtr(new MessageLoopInterruptor(&platformThread()));
     platformThread().addTaskObserver(m_pendingGCRunner.get());
     ThreadState::attach();
-    ThreadState::current()->addInterruptor(m_messageLoopInterruptor.get());
+    OwnPtr<MessageLoopInterruptor> interruptor = adoptPtr(new MessageLoopInterruptor(&platformThread()));
+    ThreadState::current()->addInterruptor(interruptor.release());
 }
 
 void WebThreadSupportingGC::shutdown()
 {
     // Ensure no posted tasks will run from this point on.
     platformThread().removeTaskObserver(m_pendingGCRunner.get());
     platformThread().scheduler()->shutdown();
 
-    ThreadState::current()->removeInterruptor(m_messageLoopInterruptor.get());
     ThreadState::detach();
     m_pendingGCRunner = nullptr;
-    m_messageLoopInterruptor = nullptr;
 }
 
 } // namespace blink