Cocoa: Delay QMimeData requests for DnD events.

We were delaying the conversion from Qt to OS X types,
but not the data request to the application.

Introduce "Eager" and "Lazy" pasteboard promises:

Eager promises request the application data immediately
and can continue to use the existing commit-promises-
on-app-exit logic. Eager promises are the default
type and will be used for copy/paste.

Lazy promises delay requesting the data from the application
for as long as possible, specifically until when 
promiseKeeper() is called. Lazy promises are used for
drag-and-drop and are not committed on application
exit.

This brings OS X DnD behavior in line with the 
Windows behavior.

[ChangeLog][OS X] Drag-and-drop QMimeData requests are
now delayed until drop time.

Task-number: QTBUG-31301
Change-Id: I8ddbba41593251f4c0c49c29492dce990066e20d
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@theqtcompany.com>

0 files changed, 0 insertions, 0 deletions