diff -r 000000000000 -r 6474c204b198 accessible/src/windows/msaa/nsWinUtils.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/accessible/src/windows/msaa/nsWinUtils.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,173 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:expandtab:shiftwidth=2:tabstop=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 "nsWinUtils.h"
+
+#include "Compatibility.h"
+#include "DocAccessible.h"
+#include "nsCoreUtils.h"
+
+#include "mozilla/Preferences.h"
+#include "nsArrayUtils.h"
+#include "nsIArray.h"
+#include "nsIDocument.h"
+#include "nsIDocShellTreeItem.h"
+#include "nsXULAppAPI.h"
+
+using namespace mozilla;
+using namespace mozilla::a11y;
+
+// Window property used by ipc related code in identifying accessible
+// tab windows.
+const wchar_t* kPropNameTabContent = L"AccessibleTabWindow";
+
+/**
+ * WindowProc to process WM_GETOBJECT messages, used in windows emulation mode.
+ */
+static LRESULT CALLBACK WindowProc(HWND hWnd, UINT msg,
+                                   WPARAM wParam, LPARAM lParam);
+
+nsRefPtrHashtable<nsPtrHashKey<void>, DocAccessible>* nsWinUtils::sHWNDCache = nullptr;
+
+already_AddRefed<nsIDOMCSSStyleDeclaration>
+nsWinUtils::GetComputedStyleDeclaration(nsIContent* aContent)
+{
+  nsIContent* elm = nsCoreUtils::GetDOMElementFor(aContent);
+  if (!elm)
+    return nullptr;
+
+  // Returns number of items in style declaration
+  nsCOMPtr<nsIDOMWindow> window =
+    do_QueryInterface(elm->OwnerDoc()->GetWindow());
+  if (!window)
+    return nullptr;
+
+  nsCOMPtr<nsIDOMCSSStyleDeclaration> cssDecl;
+  nsCOMPtr<nsIDOMElement> domElement(do_QueryInterface(elm));
+  window->GetComputedStyle(domElement, EmptyString(), getter_AddRefs(cssDecl));
+  return cssDecl.forget();
+}
+
+bool
+nsWinUtils::MaybeStartWindowEmulation()
+{
+  // Register window class that'll be used for document accessibles associated
+  // with tabs.
+  if (Compatibility::IsJAWS() || Compatibility::IsWE() ||
+      Compatibility::IsDolphin() ||
+      XRE_GetProcessType() == GeckoProcessType_Content) {
+    RegisterNativeWindow(kClassNameTabContent);
+    sHWNDCache = new nsRefPtrHashtable<nsPtrHashKey<void>, DocAccessible>(4);
+    return true;
+  }
+
+  return false;
+}
+
+void
+nsWinUtils::ShutdownWindowEmulation()
+{
+  // Unregister window call that's used for document accessibles associated
+  // with tabs.
+  if (IsWindowEmulationStarted())
+    ::UnregisterClassW(kClassNameTabContent, GetModuleHandle(nullptr));
+}
+
+bool
+nsWinUtils::IsWindowEmulationStarted()
+{
+  return sHWNDCache != nullptr;
+}
+
+void
+nsWinUtils::RegisterNativeWindow(LPCWSTR aWindowClass)
+{
+  WNDCLASSW wc;
+  wc.style = CS_GLOBALCLASS;
+  wc.lpfnWndProc = WindowProc;
+  wc.cbClsExtra = 0;
+  wc.cbWndExtra = 0;
+  wc.hInstance = GetModuleHandle(nullptr);
+  wc.hIcon = nullptr;
+  wc.hCursor = nullptr;
+  wc.hbrBackground = nullptr;
+  wc.lpszMenuName = nullptr;
+  wc.lpszClassName = aWindowClass;
+  ::RegisterClassW(&wc);
+}
+
+HWND
+nsWinUtils::CreateNativeWindow(LPCWSTR aWindowClass, HWND aParentWnd,
+                               int aX, int aY, int aWidth, int aHeight,
+                               bool aIsActive)
+{
+  HWND hwnd = ::CreateWindowExW(WS_EX_TRANSPARENT, aWindowClass,
+                                L"NetscapeDispatchWnd",
+                                WS_CHILD | (aIsActive ? WS_VISIBLE : 0),
+                                aX, aY, aWidth, aHeight,
+                                aParentWnd,
+                                nullptr,
+                                GetModuleHandle(nullptr),
+                                nullptr);
+  if (hwnd) {
+    // Mark this window so that ipc related code can identify it.
+    ::SetPropW(hwnd, kPropNameTabContent, (HANDLE)1);
+  }
+  return hwnd;
+}
+
+void
+nsWinUtils::ShowNativeWindow(HWND aWnd)
+{
+  ::ShowWindow(aWnd, SW_SHOW);
+}
+
+void
+nsWinUtils::HideNativeWindow(HWND aWnd)
+{
+  ::SetWindowPos(aWnd, nullptr, 0, 0, 0, 0,
+                 SWP_HIDEWINDOW | SWP_NOSIZE | SWP_NOMOVE |
+                 SWP_NOZORDER | SWP_NOACTIVATE);
+}
+
+LRESULT CALLBACK
+WindowProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
+{
+  // Note, this window's message handling should not invoke any call that
+  // may result in a cross-process ipc call. Doing so may violate RPC
+  // message semantics.
+
+  switch (msg) {
+    case WM_GETOBJECT:
+    {
+      if (lParam == OBJID_CLIENT) {
+        DocAccessible* document =
+          nsWinUtils::sHWNDCache->GetWeak(static_cast<void*>(hWnd));
+        if (document) {
+          IAccessible* msaaAccessible = nullptr;
+          document->GetNativeInterface((void**)&msaaAccessible); // does an addref
+          if (msaaAccessible) {
+            LRESULT result = ::LresultFromObject(IID_IAccessible, wParam,
+                                                 msaaAccessible); // does an addref
+            msaaAccessible->Release(); // release extra addref
+            return result;
+          }
+        }
+      }
+      return 0;
+    }
+    case WM_NCHITTEST:
+    {
+      LRESULT lRet = ::DefWindowProc(hWnd, msg, wParam, lParam);
+      if (HTCLIENT == lRet)
+        lRet = HTTRANSPARENT;
+      return lRet;
+    }
+  }
+
+  return ::DefWindowProcW(hWnd, msg, wParam, lParam);
+}