State download information in content description whether or not there was an update.

Talkback wasn't announcing the incremental download/install progress if the progress wasn't updated. Updated BubbleTextView to update the content description with the incremental download/install info if the progress bar should be shown.

Fixes: 149444435

Test: manual
Change-Id: I3efe6e31cec389da4119a2179a341aedd074a0b7