Adding a ShareView and ActionProvider for menus.

1. Adding a widget for sharing contenet with other applications.
   The widget orders the share targets based on previous shares.
   It displays the share target list as either a popup anchored to
   itslef or as a dialog.

2. Added a ShareDataModel that will back widgets or other classes
   that are interested in share targets for a given intent ordered
   according to share history. This class is backing the ShareView

3. Added ActionProvider mechanism for the MenuItems. The action
   provider of a menu creates the action view as well as performs
   a default action if the menu item is on the overflow menu and
   is triggered but none of the menu callback has handled that.

bug:4590827

Change-Id: Iaa4add2df2538b8c6c7edbeaf2880486d4fd75c5