diff -r 000000000000 -r 6474c204b198 xpcom/glue/nsArrayEnumerator.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/xpcom/glue/nsArrayEnumerator.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,207 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* 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/. */
+
+#include "mozilla/Attributes.h"
+
+#include "nsArrayEnumerator.h"
+
+#include "nsIArray.h"
+#include "nsISimpleEnumerator.h"
+
+#include "nsCOMArray.h"
+#include "nsCOMPtr.h"
+
+class nsSimpleArrayEnumerator MOZ_FINAL : public nsISimpleEnumerator
+{
+public:
+    // nsISupports interface
+    NS_DECL_ISUPPORTS
+
+    // nsISimpleEnumerator interface
+    NS_DECL_NSISIMPLEENUMERATOR
+
+    // nsSimpleArrayEnumerator methods
+    nsSimpleArrayEnumerator(nsIArray* aValueArray) :
+        mValueArray(aValueArray), mIndex(0) {
+    }
+
+private:
+    ~nsSimpleArrayEnumerator() {}
+
+protected:
+    nsCOMPtr<nsIArray> mValueArray;
+    uint32_t mIndex;
+};
+
+NS_IMPL_ISUPPORTS(nsSimpleArrayEnumerator, nsISimpleEnumerator)
+
+NS_IMETHODIMP
+nsSimpleArrayEnumerator::HasMoreElements(bool* aResult)
+{
+    NS_PRECONDITION(aResult != 0, "null ptr");
+    if (! aResult)
+        return NS_ERROR_NULL_POINTER;
+
+    if (!mValueArray) {
+        *aResult = false;
+        return NS_OK;
+    }
+
+    uint32_t cnt;
+    nsresult rv = mValueArray->GetLength(&cnt);
+    if (NS_FAILED(rv)) return rv;
+    *aResult = (mIndex < cnt);
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSimpleArrayEnumerator::GetNext(nsISupports** aResult)
+{
+    NS_PRECONDITION(aResult != 0, "null ptr");
+    if (! aResult)
+        return NS_ERROR_NULL_POINTER;
+
+    if (!mValueArray) {
+        *aResult = nullptr;
+        return NS_OK;
+    }
+
+    uint32_t cnt;
+    nsresult rv = mValueArray->GetLength(&cnt);
+    if (NS_FAILED(rv)) return rv;
+    if (mIndex >= cnt)
+        return NS_ERROR_UNEXPECTED;
+
+    return mValueArray->QueryElementAt(mIndex++, NS_GET_IID(nsISupports), (void**)aResult);
+}
+
+nsresult
+NS_NewArrayEnumerator(nsISimpleEnumerator* *result,
+                      nsIArray* array)
+{
+    nsSimpleArrayEnumerator* enumer = new nsSimpleArrayEnumerator(array);
+    if (enumer == nullptr)
+        return NS_ERROR_OUT_OF_MEMORY;
+
+    NS_ADDREF(*result = enumer);
+    return NS_OK;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+// enumerator implementation for nsCOMArray
+// creates a snapshot of the array in question
+// you MUST use NS_NewArrayEnumerator to create this, so that
+// allocation is done correctly
+class nsCOMArrayEnumerator MOZ_FINAL : public nsISimpleEnumerator
+{
+public:
+    // nsISupports interface
+    NS_DECL_ISUPPORTS
+
+    // nsISimpleEnumerator interface
+    NS_DECL_NSISIMPLEENUMERATOR
+
+    // nsSimpleArrayEnumerator methods
+    nsCOMArrayEnumerator() : mIndex(0) {
+    }
+
+    // specialized operator to make sure we make room for mValues
+    void* operator new (size_t size, const nsCOMArray_base& aArray) CPP_THROW_NEW;
+    void operator delete(void* ptr) {
+        ::operator delete(ptr);
+    }
+
+private:
+    ~nsCOMArrayEnumerator(void);
+
+protected:
+    uint32_t mIndex;            // current position
+    uint32_t mArraySize;        // size of the array
+    
+    // this is actually bigger
+    nsISupports* mValueArray[1];
+};
+
+NS_IMPL_ISUPPORTS(nsCOMArrayEnumerator, nsISimpleEnumerator)
+
+nsCOMArrayEnumerator::~nsCOMArrayEnumerator()
+{
+    // only release the entries that we haven't visited yet
+    for (; mIndex < mArraySize; ++mIndex) {
+        NS_IF_RELEASE(mValueArray[mIndex]);
+    }
+}
+
+NS_IMETHODIMP
+nsCOMArrayEnumerator::HasMoreElements(bool* aResult)
+{
+    NS_PRECONDITION(aResult != 0, "null ptr");
+    if (! aResult)
+        return NS_ERROR_NULL_POINTER;
+
+    *aResult = (mIndex < mArraySize);
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+nsCOMArrayEnumerator::GetNext(nsISupports** aResult)
+{
+    NS_PRECONDITION(aResult != 0, "null ptr");
+    if (! aResult)
+        return NS_ERROR_NULL_POINTER;
+
+    if (mIndex >= mArraySize)
+        return NS_ERROR_UNEXPECTED;
+
+    // pass the ownership of the reference to the caller. Since
+    // we AddRef'ed during creation of |this|, there is no need
+    // to AddRef here
+    *aResult = mValueArray[mIndex++];
+
+    // this really isn't necessary. just pretend this happens, since
+    // we'll never visit this value again!
+    // mValueArray[(mIndex-1)] = nullptr;
+    
+    return NS_OK;
+}
+
+void*
+nsCOMArrayEnumerator::operator new (size_t size, const nsCOMArray_base& aArray)
+    CPP_THROW_NEW
+{
+    // create enough space such that mValueArray points to a large
+    // enough value. Note that the initial value of size gives us
+    // space for mValueArray[0], so we must subtract
+    size += (aArray.Count() - 1) * sizeof(aArray[0]);
+
+    // do the actual allocation
+    nsCOMArrayEnumerator * result =
+        static_cast<nsCOMArrayEnumerator*>(::operator new(size));
+
+    // now need to copy over the values, and addref each one
+    // now this might seem like a lot of work, but we're actually just
+    // doing all our AddRef's ahead of time since GetNext() doesn't
+    // need to AddRef() on the way out
+    uint32_t i;
+    uint32_t max = result->mArraySize = aArray.Count();
+    for (i = 0; i<max; i++) {
+        result->mValueArray[i] = aArray[i];
+        NS_IF_ADDREF(result->mValueArray[i]);
+    }
+
+    return result;
+}
+
+nsresult
+NS_NewArrayEnumerator(nsISimpleEnumerator* *aResult,
+                      const nsCOMArray_base& aArray)
+{
+    nsCOMArrayEnumerator *enumerator = new (aArray) nsCOMArrayEnumerator();
+    if (!enumerator) return NS_ERROR_OUT_OF_MEMORY;
+
+    NS_ADDREF(*aResult = enumerator);
+    return NS_OK;
+}