diff -r 000000000000 -r 6474c204b198 gfx/2d/UserData.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gfx/2d/UserData.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,128 @@
+/* -*- 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 MOZILLA_GFX_USERDATA_H_
+#define MOZILLA_GFX_USERDATA_H_
+
+#include <stdlib.h>
+#include "Types.h"
+#include "mozilla/Assertions.h"
+
+namespace mozilla {
+namespace gfx {
+
+struct UserDataKey {
+  int unused;
+};
+
+/* this class is basically a clone of the user data concept from cairo */
+class UserData
+{
+  typedef void (*destroyFunc)(void *data);
+public:
+  UserData() : count(0), entries(nullptr) {}
+
+  /* Attaches untyped userData associated with key. destroy is called on destruction */
+  void Add(UserDataKey *key, void *userData, destroyFunc destroy)
+  {
+    for (int i=0; i<count; i++) {
+      if (key == entries[i].key) {
+        if (entries[i].destroy) {
+          entries[i].destroy(entries[i].userData);
+        }
+        entries[i].userData = userData;
+        entries[i].destroy = destroy;
+        return;
+      }
+    }
+
+    // We could keep entries in a std::vector instead of managing it by hand
+    // but that would propagate an stl dependency out which we'd rather not
+    // do (see bug 666609). Plus, the entries array is expect to stay small
+    // so doing a realloc everytime we add a new entry shouldn't be too costly
+    entries = static_cast<Entry*>(realloc(entries, sizeof(Entry)*(count+1)));
+
+    if (!entries) {
+      MOZ_CRASH();
+    }
+
+    entries[count].key      = key;
+    entries[count].userData = userData;
+    entries[count].destroy  = destroy;
+
+    count++;
+  }
+
+  /* Remove and return user data associated with key, without destroying it */
+  void* Remove(UserDataKey *key)
+  {
+    for (int i=0; i<count; i++) {
+      if (key == entries[i].key) {
+        void *userData = entries[i].userData;
+        // decrement before looping so entries[i+1] doesn't read past the end:
+        --count;
+        for (;i<count; i++) {
+          entries[i] = entries[i+1];
+        }
+        return userData;
+      }
+    }
+    return nullptr;
+  }
+
+  /* Retrives the userData for the associated key */
+  void *Get(UserDataKey *key) const
+  {
+    for (int i=0; i<count; i++) {
+      if (key == entries[i].key) {
+        return entries[i].userData;
+      }
+    }
+    return nullptr;
+  }
+
+  bool Has(UserDataKey *key)
+  {
+    for (int i=0; i<count; i++) {
+      if (key == entries[i].key) {
+        return true;
+      }
+    }
+    return false;
+  }
+
+  void Destroy()
+  {
+    for (int i=0; i<count; i++) {
+      if (entries[i].destroy) {
+        entries[i].destroy(entries[i].userData);
+      }
+    }
+    free(entries);
+    entries = nullptr;
+    count = 0;
+  }
+
+  ~UserData()
+  {
+    Destroy();
+  }
+
+private:
+  struct Entry {
+    const UserDataKey *key;
+    void *userData;
+    destroyFunc destroy;
+  };
+
+  int count;
+  Entry *entries;
+
+};
+
+}
+}
+
+#endif /* MOZILLA_GFX_USERDATA_H_ */