Some comments are copy-pasted from other, unrelated code. Documenting
a PHPUnit test file as being a "module test" is, I would argue, somewhat
pointless.
Change-Id: Iac28dc9c7b3e321b682e94c6a48efb2db41ca5f7
Changes:
- introduced new UserPreferencesChangeHandler class that listens to
PreferencesFormPreSave hook
- introduced wrapper for EventLogging extension plus NullLogger when
EventLogging extension is not availalbe
- when user changes PagePreview to disabled system will trigger
disabled event
Bug: T167365
Change-Id: I63faecb0495eb30a9fc2763e7ddf3944baf7f55a