Remove more oilpan.

sky/engine/core/dom/DocumentTest.cpp

 /*
  * Copyright (c) 2014, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 38 matching lines @@
 
 private:
     OwnPtr<DummyPageHolder> m_dummyPageHolder;
 };
 
 void DocumentTest::SetUp()
 {
     m_dummyPageHolder = DummyPageHolder::create(IntSize(800, 600));
 }
 
-class MockDocumentVisibilityObserver
-    : public DummyBase<MockDocumentVisibilityObserver>
-    , public DocumentVisibilityObserver {
-    WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(MockDocumentVisibilityObserver);
+class MockDocumentVisibilityObserver : public DocumentVisibilityObserver {
 public:
     static PassOwnPtr<MockDocumentVisibilityObserver> create(Document& document)
     {
         return adoptPtr(new MockDocumentVisibilityObserver(document));
     }
 
     virtual void trace(Visitor*) { }
 
     MOCK_METHOD1(didChangeVisibilityState, void(PageVisibilityState));
 
@@ skipping 52 matching lines @@
         ::testing::Mock::VerifyAndClearExpectations(observer2.get());
     }
 
     // observer2 destroyed
     EXPECT_CALL(*observer1, didChangeVisibilityState(PageVisibilityStateHidden)).Times(0);
     EXPECT_CALL(*observer1, didChangeVisibilityState(PageVisibilityStateVisible)).Times(1);
     page().setVisibilityState(PageVisibilityStateVisible, false);
 }
 
 } // unnamed namespace