Originally we cache mFollowingTypingSwitchPreference in fragment so in
ToggleScreenMagnificationPreferenceFragmentForSetupWizard we can set the
preference visible to false to hide it. After creating MagnificationFeaturePreferenceController,
the MagnificationFollowTypingPreferenceController can extend it and
check isInSetupWizard internally then dicide whether to hide. Therefore,
we don't need to cache mFollowingTypingSwitchPreference in fragment
and let the fragment control the preference visibility anymore.
Bug: 340721852
Flag: NONE
Test: manually
atest MagnificationFollowTypingPreferenceControllerTest
atest ToggleScreenMagnificationPreferenceFragmentForSetupWizardTest
atest ToggleScreenMagnificationPreferenceFragmentTest
Change-Id: I44f7f0589b2df3d83a27139323fc68a0561f1cfa
c9d3b39a62