question: public boolean onBackPressed ( ) { if ( doesDrawerExist ( ) ) { if ( mDrawer . isDrawerVisible ( Gravity . START ) ) { mDrawer . closeDrawer ( Gravity . START ) ; return true ; } } if ( mContentView . onBackPressed ( ) ) return true ; if ( ! mStateStack . empty ( ) ) { mStateStack . pop ( ) ; if ( ! mStateStack . empty ( ) ) { setState ( mStateStack . pop ( ) ) ; return true ; } } return false ; }
target:  Called when the user presses the back key. This is only going to be called on Phone.