diff -r 000000000000 -r 6474c204b198 xpcom/ds/nsSupportsArrayEnumerator.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/xpcom/ds/nsSupportsArrayEnumerator.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,99 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+#include "nsSupportsArrayEnumerator.h"
+#include "nsISupportsArray.h"
+
+nsSupportsArrayEnumerator::nsSupportsArrayEnumerator(nsISupportsArray* array)
+  : mArray(array), mCursor(0)
+{
+  NS_ASSERTION(array, "null array");
+  NS_ADDREF(mArray);
+}
+
+nsSupportsArrayEnumerator::~nsSupportsArrayEnumerator()
+{
+  NS_RELEASE(mArray);
+}
+
+NS_IMPL_ISUPPORTS(nsSupportsArrayEnumerator, nsIBidirectionalEnumerator, nsIEnumerator)
+
+NS_IMETHODIMP
+nsSupportsArrayEnumerator::First()
+{
+  mCursor = 0;
+  uint32_t cnt;
+  nsresult rv = mArray->Count(&cnt);
+  if (NS_FAILED(rv)) return rv;
+  int32_t end = (int32_t)cnt;
+  if (mCursor < end)
+    return NS_OK;
+  else
+    return NS_ERROR_FAILURE;
+}
+
+NS_IMETHODIMP
+nsSupportsArrayEnumerator::Next()
+{
+  uint32_t cnt;
+  nsresult rv = mArray->Count(&cnt);
+  if (NS_FAILED(rv)) return rv;
+  int32_t end = (int32_t)cnt;
+  if (mCursor < end)   // don't count upward forever
+    mCursor++;
+  if (mCursor < end)
+    return NS_OK;
+  else
+    return NS_ERROR_FAILURE;
+}
+
+NS_IMETHODIMP
+nsSupportsArrayEnumerator::CurrentItem(nsISupports **aItem)
+{
+  NS_ASSERTION(aItem, "null out parameter");
+  uint32_t cnt;
+  nsresult rv = mArray->Count(&cnt);
+  if (NS_FAILED(rv)) return rv;
+  if (mCursor >= 0 && mCursor < (int32_t)cnt) {
+    return mArray->GetElementAt(mCursor, aItem);
+  }
+  return NS_ERROR_FAILURE;
+}
+
+NS_IMETHODIMP
+nsSupportsArrayEnumerator::IsDone()
+{
+  uint32_t cnt;
+  nsresult rv = mArray->Count(&cnt);
+  if (NS_FAILED(rv)) return rv;
+  // XXX This is completely incompatible with the meaning of nsresult.
+  // NS_ENUMERATOR_FALSE is defined to be 1.  (bug 778111)
+  return (mCursor >= 0 && mCursor < (int32_t)cnt)
+    ? (nsresult)NS_ENUMERATOR_FALSE : NS_OK;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+NS_IMETHODIMP
+nsSupportsArrayEnumerator::Last()
+{
+  uint32_t cnt;
+  nsresult rv = mArray->Count(&cnt);
+  if (NS_FAILED(rv)) return rv;
+  mCursor = cnt - 1;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSupportsArrayEnumerator::Prev()
+{
+  if (mCursor >= 0)
+    --mCursor;
+  if (mCursor >= 0)
+    return NS_OK;
+  else
+    return NS_ERROR_FAILURE;
+}
+