diff -r 000000000000 -r 6474c204b198 xpcom/glue/nsInterfaceHashtable.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/xpcom/glue/nsInterfaceHashtable.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,144 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsInterfaceHashtable_h__
+#define nsInterfaceHashtable_h__
+
+#include "nsBaseHashtable.h"
+#include "nsHashKeys.h"
+#include "nsCOMPtr.h"
+
+/**
+ * templated hashtable class maps keys to interface pointers.
+ * See nsBaseHashtable for complete declaration.
+ * @param KeyClass a wrapper-class for the hashtable key, see nsHashKeys.h
+ *   for a complete specification.
+ * @param Interface the interface-type being wrapped
+ * @see nsDataHashtable, nsClassHashtable
+ */
+template<class KeyClass,class Interface>
+class nsInterfaceHashtable :
+  public nsBaseHashtable< KeyClass, nsCOMPtr<Interface> , Interface* >
+{
+public:
+  typedef typename KeyClass::KeyType KeyType;
+  typedef Interface* UserDataType;
+  typedef nsBaseHashtable< KeyClass, nsCOMPtr<Interface> , Interface* >
+          base_type;
+
+  nsInterfaceHashtable()
+  {
+  }
+  explicit nsInterfaceHashtable(uint32_t aInitSize)
+    : nsBaseHashtable<KeyClass,nsCOMPtr<Interface>,Interface*>(aInitSize)
+  {
+  }
+
+  /**
+   * @copydoc nsBaseHashtable::Get
+   * @param pData This is an XPCOM getter, so pData is already_addrefed.
+   *   If the key doesn't exist, pData will be set to nullptr.
+   */
+  bool Get(KeyType aKey, UserDataType* pData) const;
+
+  /**
+   * @copydoc nsBaseHashtable::Get
+   */
+  already_AddRefed<Interface> Get(KeyType aKey) const;
+
+  /**
+   * Gets a weak reference to the hashtable entry.
+   * @param aFound If not nullptr, will be set to true if the entry is found,
+   *               to false otherwise.
+   * @return The entry, or nullptr if not found. Do not release this pointer!
+   */
+  Interface* GetWeak(KeyType aKey, bool* aFound = nullptr) const;
+};
+
+template <typename K, typename T>
+inline void
+ImplCycleCollectionUnlink(nsInterfaceHashtable<K, T>& aField)
+{
+  aField.Clear();
+}
+
+template <typename K, typename T>
+inline void
+ImplCycleCollectionTraverse(nsCycleCollectionTraversalCallback& aCallback,
+                            const nsInterfaceHashtable<K, T>& aField,
+                            const char* aName,
+                            uint32_t aFlags = 0)
+{
+  nsBaseHashtableCCTraversalData userData(aCallback, aName, aFlags);
+
+  aField.EnumerateRead(ImplCycleCollectionTraverse_EnumFunc<typename K::KeyType,T*>,
+                       &userData);
+}
+
+//
+// nsInterfaceHashtable definitions
+//
+
+template<class KeyClass,class Interface>
+bool
+nsInterfaceHashtable<KeyClass,Interface>::Get
+  (KeyType aKey, UserDataType* pInterface) const
+{
+  typename base_type::EntryType* ent = this->GetEntry(aKey);
+
+  if (ent)
+  {
+    if (pInterface)
+    {
+      *pInterface = ent->mData;
+
+      NS_IF_ADDREF(*pInterface);
+    }
+
+    return true;
+  }
+
+  // if the key doesn't exist, set *pInterface to null
+  // so that it is a valid XPCOM getter
+  if (pInterface)
+    *pInterface = nullptr;
+
+  return false;
+}
+
+template<class KeyClass, class Interface>
+already_AddRefed<Interface>
+nsInterfaceHashtable<KeyClass,Interface>::Get(KeyType aKey) const
+{
+  typename base_type::EntryType* ent = this->GetEntry(aKey);
+  if (!ent)
+    return nullptr;
+
+  nsCOMPtr<Interface> copy = ent->mData;
+  return copy.forget();
+}
+
+template<class KeyClass,class Interface>
+Interface*
+nsInterfaceHashtable<KeyClass,Interface>::GetWeak
+  (KeyType aKey, bool* aFound) const
+{
+  typename base_type::EntryType* ent = this->GetEntry(aKey);
+
+  if (ent)
+  {
+    if (aFound)
+      *aFound = true;
+
+    return ent->mData;
+  }
+
+  // Key does not exist, return nullptr and set aFound to false
+  if (aFound)
+    *aFound = false;
+  return nullptr;
+}
+
+#endif // nsInterfaceHashtable_h__