Chrome Version: 70.0.3514.0
OS: Linux

What steps will reproduce the problem?
(1) Launch chrome with --enable-blink-features=MiddleClickAutoscroll
(2) Visit a page with an OOPIF (e.g. http://csreis.github.io/tests/cross-site-iframe.html and navigate it to simple-cross-site)
(3) Middle click just above the iframe and start scrolling down

What is the expected result?
Scrolling speed should be proportional to distance from click location

What happens instead?
Mouse moves over the OOPIF seem to be ignored for purpose of modifying scroll speed.

It seems that we're sending the mouse moves to the OOPIF under the mouse so the autoscroll speed isn't modified. When the OOPIF scrolls away and we finally mouse over the main page there's a sudden scroll jump as the page sees the large update to the mouse position.

We should lock mouse events to a single renderer while autoscroll is in progress.

A similar issue here is that if we send a mouse wheel while over the OOPIF, it'll interrupt the autoscroll but not disengage it (cursor directions are still changed but the page doesn't scroll). Mousewheel while in autoscroll - without an OOPIF - is ignored.