QTabBar implements wheelEvent to move the current index up or down. This
is useful for clicky mouse wheels, but a bad user experience when using
a kinetic wheel or touch pad, as every pixel movement will change the
current index.
Instead, scroll the entire tab bar when the wheel event comes from a
device that supports scroll phases, without changing the current index.
As drive-by's, fix the test introduced in aa09bea00c to
not leak memory or leave a test-specific style set on the QApplication
instance, which can break other tests.
Also, make relevant layout code in QTabBar respect the usesScrollButtons
property, const'ify local variables, and return an accepted QWheelEvent
if the event resulted in a change.
[ChangeLog][QtWidgets][QTabBar] Scrolling with a kinetic wheel or touch
pad scrolls the entire tab bar, without changing the current index.
Change-Id: I990e51466dd25c741877bbf0e197449f897a9efb
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>
61aa482241