Have DataObject create less copies of mime type lists.

third_party/WebKit/Source/core/clipboard/DataTransfer.cpp

 /*
  * Copyright (C) 2006, 2007, 2008 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 171 matching lines @@
     m_dataObject->setData(normalizeType(type), data);
 }
 
 // extensions beyond IE's API
 Vector<String> DataTransfer::types() const
 {
     Vector<String> types;
     if (!canReadTypes())
         return types;
 
-    ListHashSet<String> typesSet = m_dataObject->types();
-    types.appendRange(typesSet.begin(), typesSet.end());
-    return types;
+    return m_dataObject->types();
 }
 
 FileList* DataTransfer::files() const
 {
     FileList* files = FileList::create();
     if (!canReadData())
         return files;
 
     for (size_t i = 0; i < m_dataObject->length(); ++i) {
         if (m_dataObject->item(i)->kind() == DataObjectItem::FileKind) {
@@ skipping 308 matching lines @@
 DEFINE_TRACE(DataTransfer)
 {
     visitor->trace(m_dataObject);
     visitor->trace(m_dragImage);
 #if ENABLE(OILPAN)
     visitor->trace(m_dragImageElement);
 #endif
 }
 
 } // namespace blink