Bug 1546156: Don't forcibly load user32 when win32k lockdown is enabled. r=aklotz

Differential Revision: https://phabricator.services.mozilla.com/D107498

mozglue/dllservices/WindowsDllBlocklist.cpp

@@ -20,6 +20,7 @@
 #include "mozilla/TimeStamp.h"
 #include "mozilla/UniquePtr.h"
 #include "mozilla/Vector.h"
+#include "mozilla/WindowsProcessMitigations.h"
 #include "mozilla/WindowsVersion.h"
 #include "mozilla/WinHeaderOnlyUtils.h"
 #include "nsWindowsHelpers.h"
@@ -672,7 +673,7 @@ MFBT_API void DllBlocklist_Initialize(uint32_t aInitFlags) {
   // If someone injects a thread early that causes user32.dll to load off the
   // main thread this causes issues, so load it as soon as we've initialized
   // the block-list. (See bug 1400637)
-  if (!sUser32BeforeBlocklist) {
+  if (!sUser32BeforeBlocklist && !IsWin32kLockedDown()) {
     ::LoadLibraryW(L"user32.dll");
   }