Adding a native widget such as QGLWidget often causes
other widgets to become native, through native ancestor
and sibling propagation.
This includes QFocusFrame, which typically sits on
top of item views. QFocusFrame is mostly transparent
(except for the frame) and also has the WA_TransparentForMouseEvents
flag set. Its window has the corresponding
WindowTransparentForInput flag set.
Cocoa does not know about WindowTransparentForInput.
Forward the drag calls to the correct window.
Task-number: QTBUG-37077
Change-Id: I02201c7027915b1e82d0cd7e9c2e787ca6b2338b
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>