Fix import errors.

Author: hwf1324

addon/globalPlugins/viewerFrame.py

@@ -9,6 +9,7 @@
 import gui.guiHelper
 import wx
 import wx.py
+from gui.dpiScalingHelper import DpiScalingHelperMixinWithoutInit
 from gui.nvdaControls import AutoWidthColumnListCtrl
 from NVDAObjects import NVDAObject