easy-signin: Use ExtendedAuthenticator for unlock.
- Use ExtendedAuthenticator for unlock so that cryptohome
CheckKeyEx is used to check all keys. This solves the
problem in 419532 that password based key is not checked
when signing in using the phone.
- Make ExtendedAuthenticator an interface.
- Implementation is moved to ExtendedAuthenticatorImpl.
- Added a FakeExtendedAuthenticator.
- Make ScreenLockerTester::InjectMockAuthenticator to mock
ExtendedAuthenticator as well.
BUG=419532, 351268
TBR=pam@chromium.org for supervised_user change
Review URL: https://codereview.chromium.org/
642753003
Cr-Commit-Position: refs/heads/master@{#299602}