user32/tests: Use empty_message_queue with timeouts.

dlls/user32/tests/input.c

@@ -360,11 +360,24 @@ static void test_Input_whitebox(void)
     DestroyWindow(hWndTest);
 }
 
-static void empty_message_queue(void) {
+/* try to make sure pending X events have been processed before continuing */
+static void empty_message_queue(void)
+{
     MSG msg;
-    while(PeekMessage(&msg, NULL, 0, 0, PM_REMOVE)) {
-        TranslateMessage(&msg);
-        DispatchMessage(&msg);
+    int diff = 200;
+    int min_timeout = 50;
+    DWORD time = GetTickCount() + diff;
+
+    while (diff > 0)
+    {
+        if (MsgWaitForMultipleObjects(0, NULL, FALSE, min_timeout, QS_ALLINPUT) == WAIT_TIMEOUT) break;
+        while (PeekMessage(&msg, 0, 0, 0, PM_REMOVE))
+        {
+            TranslateMessage(&msg);
+            DispatchMessage(&msg);
+        }
+        diff = time - GetTickCount();
+        min_timeout = 20;
     }
 }