Find it and CL did not provide any possible suspects.
Using Code Search for the file, "content_autofill_driver.cc" assigning to the concern owner.

Suspecting Commit#
https://chromium.googlesource.com/chromium/src/+/e0a9f158f10a9f5ee5d21d571518ff46929af89f

@blundell -- Could you please look into the issue, kindly re-assign if this is not related to your changes.
Thank You.

It's not that CL (just a renaming CL). To mathp@ for triage.

Assigning to kenrb@ who last touched (and added) the function.

The most likely CL responsible for the regression is https://chromium.googlesource.com/chromium/src/+/9431efdc7b0146ef74f75ce160f2ba343ca2d550.

lfg@: Your CL shouldn't have caused this, so there is probably a pre-existing underlying bug, but would you mind investigating?

I've looked into this today, and I'm unable to reproduce the crash. I've re-ran the clusterfuzz task and it also can't reproduce it anymore.

Here's a summary of what I found:

The RenderWidgetHostView can be destroyed in 3 places:
1) RenderFrameHostManager::DiscardUnusedFrame
   - This can't be the source, since it shouldn't be possible to interact with the pending RFH, so that RFH's autofill agent can't be the one sending the message.
2) RenderFrameHostManager::CommitPending
   - Can't be this one either, since early in the function we call FrameTreeNode::ResetForNewProcess, which destroys the frame and the autofill driver.
3) RenderWidgetHost::OnRenderProcessGone
   - I don't think it's this one, as I wouldn't expect mojo to deliver messages after the render process is destroyed. Also, in this case, I would expect clusterfuzz to find an earlier renderer crash.

For now, I'll close this as WontFix.