Currently the ui::EventHandler logic is being refactored out of RenderWidgetHostViewAura, so that it can be shared with RenderWidgetHostViewMus.  (https://codereview.chromium.org/2317333002/)

During this we noticed that there is significant Windows specific logic. It would be good to try to refactor this out of the new RenderWidgetHostViewEventHandler into a Windows specific subclass.