diff -r 000000000000 -r 6474c204b198 widget/windows/WindowHook.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/widget/windows/WindowHook.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,81 @@
+/* -*- 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_WindowHook_h__
+#define __mozilla_WindowHook_h__
+
+#include <windows.h>
+
+#include <nsHashKeys.h>
+#include <nsClassHashtable.h>
+#include <nsTArray.h>
+
+#include "nsAppShell.h"
+
+class nsWindow;
+
+namespace mozilla {
+namespace widget {
+
+struct MSGResult;
+
+class WindowHook {
+public:
+
+  // It is expected that most callbacks will return false
+  typedef bool (*Callback)(void *aContext, HWND hWnd, UINT nMsg,
+                             WPARAM wParam, LPARAM lParam, LRESULT *aResult);
+
+  nsresult AddHook(UINT nMsg, Callback callback, void *context);
+  nsresult RemoveHook(UINT nMsg, Callback callback, void *context);
+  nsresult AddMonitor(UINT nMsg, Callback callback, void *context);
+  nsresult RemoveMonitor(UINT nMsg, Callback callback, void *context);
+
+private:
+  struct CallbackData {
+    Callback cb;
+    void *context;
+
+    CallbackData() : cb(nullptr), context(nullptr) {}
+    CallbackData(Callback cb, void *ctx) : cb(cb), context(ctx) {}
+    bool Invoke(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam,
+                  LRESULT *aResult);
+    bool operator== (const CallbackData &rhs) const {
+      return cb == rhs.cb && context == rhs.context;
+    }
+    bool operator!= (const CallbackData &rhs) const {
+      return !(*this == rhs);
+    }
+    operator bool () const {
+      return !!cb;
+    }
+  };
+
+  typedef nsTArray<CallbackData> CallbackDataArray;
+  struct MessageData {
+    UINT nMsg;
+    CallbackData hook;
+    CallbackDataArray monitors;
+  };
+
+  bool Notify(HWND hWnd, UINT nMsg, WPARAM wParam, LPARAM lParam,
+              MSGResult& aResult);
+
+  MessageData *Lookup(UINT nMsg);
+  MessageData *LookupOrCreate(UINT nMsg);
+  void DeleteIfEmpty(MessageData *data);
+
+  typedef nsTArray<MessageData> MessageDataArray;
+  MessageDataArray mMessageData;
+
+  // For Notify
+  friend class ::nsWindow;
+};
+
+}
+}
+
+#endif // __mozilla_WindowHook_h__