Bug 1539581 - Cleanup use of RegisterWindowMessgae in nsAppShell. r=bobowen

Differential Revision: https://phabricator.services.mozilla.com/D25235

--HG--
extra : moz-landing-system : lando

ipc/glue/WindowsMessageLoop.cpp

@@ -76,12 +76,8 @@ using namespace mozilla::ipc::windows;
 extern const wchar_t* kPropNameTabContent;
 #endif
 
-// widget related message id constants we need to defer
-namespace mozilla {
-namespace widget {
+// widget related message id constants we need to defer, see nsAppShell.
 extern UINT sAppShellGeckoMsgId;
-}
-}  // namespace mozilla
 
 namespace {
 
@@ -390,7 +386,7 @@ ProcessOrDeferMessage(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam) {
     default: {
       // Unknown messages only are logged in debug builds and sent to
       // DefWindowProc.
-      if (uMsg && uMsg == mozilla::widget::sAppShellGeckoMsgId) {
+      if (uMsg && uMsg == sAppShellGeckoMsgId) {
         // Widget's registered native event callback
         deferred = new DeferredSendMessage(hwnd, uMsg, wParam, lParam);
       }

widget/windows/nsAppShell.cpp

@@ -157,13 +157,11 @@ SingleNativeEventPump::AfterProcessNextEvent(nsIThreadInternal* aThread,
   return NS_OK;
 }
 
-namespace mozilla {
-namespace widget {
-// Native event callback message.
-UINT sAppShellGeckoMsgId = RegisterWindowMessageW(L"nsAppShell:EventID");
-}  // namespace widget
-}  // namespace mozilla
-
+// RegisterWindowMessage values
+// Native event callback message
+const wchar_t* kAppShellGeckoEventId = L"nsAppShell:EventID";
+UINT sAppShellGeckoMsgId;
+// Taskbar button creation message
 const wchar_t* kTaskbarButtonEventId = L"TaskbarButtonCreated";
 UINT sTaskbarButtonCreatedMsg;
 
@@ -331,8 +329,13 @@ nsresult nsAppShell::Init() {
 
   // The hidden message window is used for interrupting the processing of native
   // events, so that we can process gecko events. Therefore, we only need it if
-  // we are processing native events.
+  // we are processing native events. Disabling this is required for win32k
+  // syscall lockdown.
   if (XRE_UseNativeEventProcessing()) {
+    sAppShellGeckoMsgId = ::RegisterWindowMessageW(kAppShellGeckoEventId);
+    NS_ASSERTION(sAppShellGeckoMsgId,
+                 "Could not register hidden window event message!");
+
     mLastNativeEventScheduled = TimeStamp::NowLoRes();
 
     WNDCLASSW wc;