Fix a crash in PasswordGenerationPopupControllerImpl caused by double deletion.

The flow of the crash
- PasswordManager::OnGeneratedPasswordAccepted is called when a generated password is accepted.
- It can bring up the "Update Password?" bubble
- Focus lost event is happening, the dropdown is closed, the controller is destroyed.
- PasswordManager::OnGeneratedPasswordAccepted finishes.
- PasswordGenerationPopupControllerImpl tries to hide the UI again but everything is gone already.

Bug: 995321
Change-Id: I791c969ea6af1b6fc305219a5c22d49424ab38ab
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1762214
Reviewed-by: Ioana Pandele <ioanap@chromium.org>
Commit-Queue: Vasilii Sukhanov <vasilii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#688556}
5 files changed