RenderWidgetHost should be able to send events to InputEventRouter.
This is needed to fix the problem in interaction with cross-origin iframes while in VR browsing mode. Moreover, the refactoring will remove repeated code in render_widget_host_view_android, render_widget_host_view_aura, and render_widget_host_view_mac.  Event routing has some similarities between different platforms, it can be merged into 
render_widget_host_impl. At very least the logic for deciding whether should_route_event (https://cs.chromium.org/chromium/src/content/browser/renderer_host/render_widget_host_view_android.cc?dr=CSs&l=1957, https://cs.chromium.org/chromium/src/content/browser/renderer_host/render_widget_host_view_event_handler.cc?dr=CSs&l=373) or not can be merged.