gdiplus: Partially implemented GdipTestControl.
diff --git a/include/gdiplusflat.h b/include/gdiplusflat.h
index cbb59e5..03980ea 100644
--- a/include/gdiplusflat.h
+++ b/include/gdiplusflat.h
@@ -537,6 +537,8 @@
 GpStatus WINGDIPAPI GdipSetAdjustableArrowCapMiddleInset(GpAdjustableArrowCap*,REAL);
 GpStatus WINGDIPAPI GdipSetAdjustableArrowCapWidth(GpAdjustableArrowCap*,REAL);
 
+GpStatus WINGDIPAPI GdipTestControl(GpTestControlEnum,void*);
+
 #ifdef __cplusplus
 }
 #endif