[Win] WTF::RunLoop: RegisterClass has to be called in the main thread…

… before creating other threads

https://bugs.webkit.org/show_bug.cgi?id=255624

Reviewed by Don Olmstead.

CreateWindow was randomly failing in the GPU process for WebGL tests
for Windows port. This seems to be a theading issue of calling
CreateWindow in a different thread rather than one called
RegisterClass. RegisterClass has to be called in the main thread
before creating other threads. Reverted 228617@main.

* Source/WTF/wtf/win/MainThreadWin.cpp:
(WTF::initializeMainThreadPlatform):
* Source/WTF/wtf/win/RunLoopWin.cpp:
(WTF::RunLoop::registerRunLoopMessageWindowClass):
(WTF::RunLoop::RunLoop):

Canonical link: https://commits.webkit.org/263194@main

Source/WTF/wtf/win/MainThreadWin.cpp

@@ -43,6 +43,7 @@ void initializeMainThreadPlatform()
 {
     s_mainThread = Thread::currentID();
     Thread::initializeCurrentThreadInternal("Main Thread");
+    RunLoop::registerRunLoopMessageWindowClass();
 }
 
 bool isMainThread()

Source/WTF/wtf/win/RunLoopWin.cpp

@@ -90,20 +90,16 @@ void RunLoop::stop()
 
 void RunLoop::registerRunLoopMessageWindowClass()
 {
-    static std::once_flag onceKey;
-    std::call_once(onceKey, [&] {
-        WNDCLASS windowClass = { };
-        windowClass.lpfnWndProc     = RunLoop::RunLoopWndProc;
-        windowClass.cbWndExtra      = sizeof(RunLoop*);
-        windowClass.lpszClassName   = kRunLoopMessageWindowClassName;
-        bool result = ::RegisterClass(&windowClass);
-        RELEASE_ASSERT(result);
-    });
+    WNDCLASS windowClass = { };
+    windowClass.lpfnWndProc = RunLoop::RunLoopWndProc;
+    windowClass.cbWndExtra = sizeof(RunLoop*);
+    windowClass.lpszClassName = kRunLoopMessageWindowClassName;
+    bool result = ::RegisterClass(&windowClass);
+    RELEASE_ASSERT(result);
 }
 
 RunLoop::RunLoop()
 {
-    registerRunLoopMessageWindowClass();
     m_runLoopMessageWindow = ::CreateWindow(kRunLoopMessageWindowClassName, nullptr, 0,
         CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, HWND_MESSAGE, nullptr, nullptr, this);
     RELEASE_ASSERT(::IsWindow(m_runLoopMessageWindow));