TextView not respecting "speak passwords" setting when adding before text to events.

1. If the speak passwords settings is on, the accessibility events emitted from a
   TextView should contain the text and before text of the source. The settings
   shows the users consent to put the source's text in the event. While the code
   that populates the current text in the accessibility event respects the
   setting, the one that populates the before text does not. As a result the
   fact that the user has typed a letter cannot be echoed by an accessibility
   service.

bug:7468768

Change-Id: I7580c37936d742f42653315b2591e268a634d22b