diff -r 000000000000 -r 6474c204b198 accessible/src/base/AccCollector.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/accessible/src/base/AccCollector.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,117 @@
+/* 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 "AccCollector.h"
+
+#include "Accessible.h"
+
+using namespace mozilla::a11y;
+
+////////////////////////////////////////////////////////////////////////////////
+// nsAccCollector
+////////////////////////////////////////////////////////////////////////////////
+
+AccCollector::
+  AccCollector(Accessible* aRoot, filters::FilterFuncPtr aFilterFunc) :
+  mFilterFunc(aFilterFunc), mRoot(aRoot), mRootChildIdx(0)
+{
+}
+
+AccCollector::~AccCollector()
+{
+}
+
+uint32_t
+AccCollector::Count()
+{
+  EnsureNGetIndex(nullptr);
+  return mObjects.Length();
+}
+
+Accessible*
+AccCollector::GetAccessibleAt(uint32_t aIndex)
+{
+  Accessible* accessible = mObjects.SafeElementAt(aIndex, nullptr);
+  if (accessible)
+    return accessible;
+
+  return EnsureNGetObject(aIndex);
+}
+
+int32_t
+AccCollector::GetIndexAt(Accessible* aAccessible)
+{
+  int32_t index = mObjects.IndexOf(aAccessible);
+  if (index != -1)
+    return index;
+
+  return EnsureNGetIndex(aAccessible);
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// nsAccCollector protected
+
+Accessible*
+AccCollector::EnsureNGetObject(uint32_t aIndex)
+{
+  uint32_t childCount = mRoot->ChildCount();
+  while (mRootChildIdx < childCount) {
+    Accessible* child = mRoot->GetChildAt(mRootChildIdx++);
+    if (!(mFilterFunc(child) & filters::eMatch))
+      continue;
+
+    AppendObject(child);
+    if (mObjects.Length() - 1 == aIndex)
+      return mObjects[aIndex];
+  }
+
+  return nullptr;
+}
+
+int32_t
+AccCollector::EnsureNGetIndex(Accessible* aAccessible)
+{
+  uint32_t childCount = mRoot->ChildCount();
+  while (mRootChildIdx < childCount) {
+    Accessible* child = mRoot->GetChildAt(mRootChildIdx++);
+    if (!(mFilterFunc(child) & filters::eMatch))
+      continue;
+
+    AppendObject(child);
+    if (child == aAccessible)
+      return mObjects.Length() - 1;
+  }
+
+  return -1;
+}
+
+void
+AccCollector::AppendObject(Accessible* aAccessible)
+{
+  mObjects.AppendElement(aAccessible);
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// EmbeddedObjCollector
+////////////////////////////////////////////////////////////////////////////////
+
+int32_t
+EmbeddedObjCollector::GetIndexAt(Accessible* aAccessible)
+{
+  if (aAccessible->mParent != mRoot)
+    return -1;
+
+  if (aAccessible->mIndexOfEmbeddedChild != -1)
+    return aAccessible->mIndexOfEmbeddedChild;
+
+  return mFilterFunc(aAccessible) & filters::eMatch ?
+    EnsureNGetIndex(aAccessible) : -1;
+}
+
+void
+EmbeddedObjCollector::AppendObject(Accessible* aAccessible)
+{
+  aAccessible->mIndexOfEmbeddedChild = mObjects.Length();
+  mObjects.AppendElement(aAccessible);
+}