Add SH_ItemView_ScrollMode style hint and use it in QMacStyle

On OS X, the default scrolling mode of item views should be
per pixel instead of per item. We enforce this through a new
style hint. On all other platforms, the behavior remains the
same.

It's still possible to override the style hint by using the
regular scroll mode setters. Any subsequent style change will
result in a no-op once the setters have been called and until
the properties are reset.

Some auto-tests had to be update to to take the new behavior
into account.

[ChangeLog][QtWidgets][Styles] Added SH_ItemView_ScrollMode
style hint.

[ChangeLog][QtWidgets][Item Views] Item views scroll per pixel
on OS X now.

[ChangeLog][QtWidgets][Item Views] QAbstractItemView::verticalScrollMode
and QAbstractItemView::horizontalScrollMode are now resettable.

Change-Id: I3f923275c99aa4389323b52fc1c5455fe71f8d73
Task-number: QTBUG-50102
Reviewed-by: Jake Petroules <jake.petroules@theqtcompany.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/tests/auto/widgets/itemviews/qtreeview/tst_qtreeview.cpp b/tests/auto/widgets/itemviews/qtreeview/tst_qtreeview.cpp
index e21aedee1e..137f18e23a 100644
--- a/tests/auto/widgets/itemviews/qtreeview/tst_qtreeview.cpp
+++ b/tests/auto/widgets/itemviews/qtreeview/tst_qtreeview.cpp
@@ -503,7 +503,7 @@ void tst_QTreeView::construction()
     QCOMPARE(view.sizeHintForRow(1), -1);
     QVERIFY(!view.tabKeyNavigation());
     QCOMPARE(view.textElideMode(), Qt::ElideRight);
-    QCOMPARE(view.verticalScrollMode(), QAbstractItemView::ScrollPerItem);
+    QCOMPARE(static_cast<int>(view.verticalScrollMode()), view.style()->styleHint(QStyle::SH_ItemView_ScrollMode, 0, &view));
     QCOMPARE(view.visualRect(QModelIndex()), QRect());
 
     // QTreeView properties