Bug 677883 - Bypass deferred message processing for accessible tab windows. Fixes occasional wm_getobject query failures, which must be responded to. r=davidb

accessible/src/msaa/nsAccessNodeWrap.cpp

@@ -743,6 +743,10 @@ nsRefPtrHashtable<nsVoidPtrHashKey, nsDocAccessible> nsAccessNodeWrap::sHWNDCach
 LRESULT CALLBACK
 nsAccessNodeWrap::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:
     {

accessible/src/msaa/nsWinUtils.cpp

@@ -46,6 +46,10 @@
 #include "nsArrayUtils.h"
 #include "nsIDocShellTreeItem.h"
 
+// Window property used by ipc related code in identifying accessible
+// tab windows.
+const PRUnichar* kPropNameTabContent = L"AccessibleTabWindow";
+
 HRESULT
 nsWinUtils::ConvertToIA2Array(nsIArray *aGeckoArray, IUnknown ***aIA2Array,
                               long *aIA2ArrayLen)
@@ -149,7 +153,7 @@ nsWinUtils::CreateNativeWindow(LPCWSTR aWindowClass, HWND aParentWnd,
                                int aX, int aY, int aWidth, int aHeight,
                                bool aIsActive)
 {
-  return ::CreateWindowExW(WS_EX_TRANSPARENT, aWindowClass,
+  HWND hwnd = ::CreateWindowExW(WS_EX_TRANSPARENT, aWindowClass,
                                 L"NetscapeDispatchWnd",
                                 WS_CHILD | (aIsActive ? WS_VISIBLE : 0),
                                 aX, aY, aWidth, aHeight,
@@ -157,6 +161,11 @@ nsWinUtils::CreateNativeWindow(LPCWSTR aWindowClass, HWND aParentWnd,
                                 NULL,
                                 GetModuleHandle(NULL),
                                 NULL);
+  if (hwnd) {
+    // Mark this window so that ipc related code can identify it.
+    ::SetPropW(hwnd, kPropNameTabContent, (HANDLE)1);
+  }
+  return hwnd;
 }
 
 void

ipc/glue/WindowsMessageLoop.cpp

@@ -101,6 +101,8 @@ using namespace mozilla::ipc::windows;
 
 // pulled from widget's nsAppShell
 extern const PRUnichar* kAppShellEventId;
+// pulled from accessibility's win utils
+extern const PRUnichar* kPropNameTabContent;
 
 namespace {
 
@@ -379,6 +381,12 @@ WindowIsDeferredWindow(HWND hWnd)
     return false;
   }
 
+  // Tab content creates a window that responds to accessible WM_GETOBJECT
+  // calls. This window can safely be ignored.
+  if (::GetPropW(hWnd, kPropNameTabContent)) {
+    return false;
+  }
+
   // Common mozilla windows we must defer messages to.
   nsDependentString className(buffer, length);
   if (StringBeginsWith(className, NS_LITERAL_STRING("Mozilla")) ||