Showing default activity in activity chooser view only if enough space.

1. While a default target is very convenient, having two targets for the
   widget on a phone takes too much space and the apps do not have room
   to add other essential affordances to the action bar. Making the default
   activity show only of the screen is large enough - the action bar
   accommodates at least four targets i.e. 500dip.

2. Fixed a bug where changing the backing model of an ActivityChooserView
   when the view is not shown did not remove the observer for the old
   model, hence the View can get into a state where it responds to changes
   of two models while presenting only one. Also in such a case the view
   would leak since the singleton model will keep a handle to it.

3. Updated the documentation of share action provider to explain how a
   a developer can change the backing history file and refresh the UI
   based on the historical data in that file.

bug:6447692

Change-Id: Id5c9e54cd5df322ded8574ba028cb680e628243b

0 files changed, 0 insertions, 0 deletions