GitLab

Instead of trying to forward fix, dumbly revert the cause of crashes.
Hopefully, just in time before M89 branch cut.

This revert will fix:
- https://crbug.com/1153966
- https://crbug.com/1153961

This revert part of:
https://chromium-review.googlesource.com/c/chromium/src/+/2548022
```
Retire ScopedObserver in /chrome/browser/ui/views.

ScopedObserver is being deprecated in favor of two new classes:
- base::ScopedObservation for observers that only ever observe
  a single source.
- base::ScopedMultiSourceObservation for observers that do or may
  observe more than a single source.

This CL was uploaded by git cl split.

R=bsep@chromium.org

Bug: 1145565
```

There was an existing bug. Unexpectedly, HungPagesTableModel::
InitForWebContents() can be called twice. See
https://crbug.com/1165917. For some reasons, this didn't resulted in any
crashes...

...until the reverted patch cames in.
The old base::ScopedObserver was supporting multiple observations. The
new one: base::ScopedObservation doesn't. As a result, if
base::ScopedObservation::Observe is called twice, then RemoveObserver
will be called only once instead of two, causing the issue.

Bug: 1153966,1153961
Change-Id: Iecc8e8e0e9fa387795ce55b4414d1d871cc4c9a0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2625867Reviewed-by: Bret Sepulveda <bsep@chromium.org>
Commit-Queue: Arthur Sonzogni <arthursonzogni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#842940}