Not stated clearly, but seems FileManagerPrivate.addMount does:
- reply with success regardless of if mounting was successful or not. The return result contains VolumeInfo.
- lately 'mount' event will be issued with VolumeMetadata (if success) or error otherwise.

https://cs.chromium.org/chromium/src/third_party/closure_compiler/externs/file_manager_private.js?q=file:file_manager+addmount&sq=package:chromium&l=386

If this is correct, I think we should state it in the function's comment as it's not obvious what happens upon getting the callback from addMount.

Changing this to Pri-3, Task, as this is now not blocking the issue.

I think we can resolve Issue 798024 by https://chromium-review.googlesource.com/c/chromium/src/+/896765, which just avoids error.

This is a proposal to cleanup the logic by these changes:
- store mount source path in VolumeManager (or somewhere in JS side)
- stop invoking fileManagerPrivate.addMount when duplicated mount attempt was detected
- Files app should trigger folder navigation, to the mounted volume. (currently it is done by receiving 'mount' event which notifies mount completion event.)

I think this is blocked by (if not a duplicate of) issue 810205.

I have an idea on how to fix this, but it is low priority at the moment.

I'll put more details on the other bug.