Remove unnecessary includes from dom.

third_party/WebKit/Source/core/dom/DocumentStyleSheetCollector.h

 /*
  * 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.
  *     * Neither the name of Google Inc. nor the names of its
@@ skipping 11 matching lines @@
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef DocumentStyleSheetCollector_h
 #define DocumentStyleSheetCollector_h
 
 #include "platform/heap/Handle.h"
 #include "wtf/HashSet.h"
-#include "wtf/RefPtr.h"
 #include "wtf/Vector.h"
 
 namespace blink {
 
 class CSSStyleSheet;
 class Document;
 class StyleSheet;
 class StyleSheetCollection;
 
 class DocumentStyleSheetCollector {
@@ skipping 28 matching lines @@
 };
 
 class ImportedDocumentStyleSheetCollector final : public DocumentStyleSheetCollector {
 public:
     ImportedDocumentStyleSheetCollector(DocumentStyleSheetCollector&, HeapVector<Member<StyleSheet>>&);
 };
 
 } // namespace blink
 
 #endif // DocumentStyleSheetCollector_h