DispatchMouseEvent() assumes event coords are in target-view coords (see 
https://cs.chromium.org/chromium/src/content/browser/renderer_host/render_widget_host_input_event_router.h?rcl=41223362de706e400ebf8adbeeb86bc7d3b6abab&l=179)

but SendMouseEnterOrLeaveEvents() assumes they are in root-view coords (see here:
https://cs.chromium.org/chromium/src/content/browser/renderer_host/render_widget_host_input_event_router.cc?rcl=41223362de706e400ebf8adbeeb86bc7d3b6abab&l=661).

Would it be simpler to require all RWHIER::DispatchXEvent() fcns take the events with root-view coords? (See proposed CL here: https://chromium-review.googlesource.com/c/chromium/src/+/855118)