This directory contains files for managing ChromeOS users. Historically, the code manages both user and user sessions. There is an on-going effort to move user session related code into //components/session_manager.
UserManager is the interface for managing ChromeOS users. UserManagerBase is a base implementation of the interface. There is also a UserManagerInterface in Chrome code that provides additional UserManager interface that deals with policy. ChromeUserManager inherits UserManagerBase and UserManagerInterface it provide a base implementation. Finally, the concrete instance used is ChromeUserManagerImpl derived from ChromeUserManager.
ChromeUserManagerImpl is created at the PreProfileInit stage and destroyed at the PostMainMessageLoopRun stage, via BrowserProcessPlatformPart::InitializeChromeUserManager() and BrowserProcessPlatformPart::DestroyChromeUserManager.
This directory contains the UserDirectoryIntegrityManager class. This class is responsible for detecting when a user did not completely complete the onboarding flow and crashed before adding an auth factor. This can leave the user in an inconsistent state as their home directory will be encrypted with no auth factors added.
UserDirectoryIntegrityManager writes the user's email to local state before creating the user home directory and erases it after adding a successful auth factor. Those operations are initiated from MountPerformer::CreateNewUser and AuthFactorEditor::OnAddCredentials respectively.