Add facility to run callbacks on the window thread

Windows/MainWindow.cpp

@@ -764,6 +764,13 @@ namespace MainWindow
 			}
 			break;
 
+		case WM_USER_RUN_CALLBACK:
+		{
+			auto callback = reinterpret_cast<void (*)(void *window, void *userdata)>(wParam);
+			void *userdata = reinterpret_cast<void *>(lParam);
+			callback(hWnd, userdata);
+			break;
+		}
 		case WM_USER_GET_BASE_POINTER:
 			Reporting::NotifyDebugger();
 			switch (lParam) {
@@ -1135,4 +1142,8 @@ namespace MainWindow
 		return g_isFullscreen;
 	}
 
+	void RunCallbackInWndProc(void (*callback)(void *, void *), void *userdata) {
+		PostMessage(hwndMain, WM_USER_RUN_CALLBACK, reinterpret_cast<WPARAM>(callback), reinterpret_cast<LPARAM>(userdata));
+	}
+
 }  // namespace