API CHANGE: startDrag() now takes "int flags" instead of "boolean localOnly"

There will be, in the future, a flag (View.DRAG_FLAG_GLOBAL) that means
for the drag to be cross-application.  For now that flag constant is @hide
and furthermore the server-side implementation strips it, enforcing
local-only drags.

Change-Id: I8db840480ab90e18a5b8ecf29d62b4e6eafd405e