Don't try to use ManagePasswordsBubbleModel if the password bubble was closed.
The bubble may be closed by some navigation in the content area. However, if the user pressed a button before closing and released after then the button action is still sent. Moreover, all the objects like NSWindow, NSWindowController, NSViewController are still alive. The UI code should not ping ManagePasswordsBubbleModel which is actually destroyed.
BUG=
579726
Committed:
https://crrev.com/a3aaa89baf57b6cbbf4905ccbaccc4aedb08b4e7
Cr-Commit-Position: refs/heads/master@{#371513}