Simplify ownership of a ThreadState's interruptors.

Source/platform/WebThreadSupportingGC.h

 // 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.
 
 #ifndef WebThreadSupportingGC_h
 #define WebThreadSupportingGC_h
 
 #include "platform/heap/glue/MessageLoopInterruptor.h"
 #include "platform/heap/glue/PendingGCRunner.h"
 #include "public/platform/Platform.h"
@@ skipping 47 matching lines @@
     WebThread& platformThread() const
     {
         ASSERT(m_thread);
         return *m_thread;
     }
 
 private:
     explicit WebThreadSupportingGC(const char*);
 
     OwnPtr<PendingGCRunner> m_pendingGCRunner;
-    OwnPtr<MessageLoopInterruptor> m_messageLoopInterruptor;
 
     // FIXME: This has to be last because of crbug.com/401397.
     // A WorkerThread might get deleted before it had a chance to properly
     // shut down. By deleting the WebThread first, we can guarantee that
     // no pending tasks on the thread might want to access any of the other
     // members during the WorkerThread's destruction.
     OwnPtr<WebThread> m_thread;
 };
 
 }
 
 #endif