Fix NPE while running UserSwitcherController The mRootView in UserSwitcherController is not initialized while running the test, fulfill the dependencies and initialize it before testing the function. Bug: 206333323 Test: atest com.android.systemui.statusbar.policy.UserSwitcherControllerTest Change-Id: I807ac2d1279b4f48c94e5d9ccd51f3a43d5884c5