Remove more oilpan.

sky/engine/core/testing/NullExecutionContext.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 NullExecutionContext_h
 #define NullExecutionContext_h
 
 #include "core/dom/ExecutionContext.h"
 #include "core/events/EventQueue.h"
 #include "platform/heap/Handle.h"
 #include "platform/weborigin/KURL.h"
 #include "wtf/RefCounted.h"
 
 namespace blink {
 
 class NullExecutionContext final : public RefCounted<NullExecutionContext>, public ExecutionContext {
-    WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(NullExecutionContext);
 public:
     NullExecutionContext();
 
     virtual EventQueue* eventQueue() const override { return m_queue.get(); }
 
     void trace(Visitor* visitor)
     {
         visitor->trace(m_queue);
         ExecutionContext::trace(visitor);
     }
@@ skipping 14 matching lines @@
 
 private:
     OwnPtr<EventQueue> m_queue;
 
     KURL m_dummyURL;
 };
 
 } // namespace blink
 
 #endif // NullExecutionContext_h