Ensure autoscroll ends when navigating to a different page

This CL adds a call to AutoscrollController::StopMiddleClickAutoscroll
when a navigation to a different page happens. When changing pages,
multiple things can happen:
a) The current renderer process is destroyed and a new one is created
for the new page.
b) The renderer process is recycled to show the new webpage
c) A new renderer process is created to show the new webpage, and the
current process is cached in case the user navigates back to the
previous page.

When (b) and (c) happen, autoscroll is not necessarily correctly reset,
and the renderer process never notifies the browser process that the
autoscroll ended. When this happens, the browser process remains in
an incorrect state and stops forwarding mouse events to the renderer
process, and the tab becomes unusable.

To easily repro this issue:
1) Open devtools, network tab, set throttling to 3G (makes it easier to
   start scrolling before the page changes)
2) Go to any scrollable page with a link (like a Google search)
3) Click on it, and before the browser loads the new page press the
   middle mouse button and start scrolling.
4) The tab becomes unusable. Keyboard commands (like arrow scrolling)
   and the browser's UI still work, but no mouse events are forwarded.

Bug: 381696865
Change-Id: I01cab52575044a2d99ac03e8a106c705dd489c10
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6352897
Reviewed-by: Robert Flack <flackr@chromium.org>
Reviewed-by: Olga Gerchikov <gerchiko@microsoft.com>
Commit-Queue: Gaston Rodriguez <gastonr@microsoft.com>
Cr-Commit-Position: refs/heads/main@{#1436920}