Use a dedicated timer for the animation driver.

QUnifiedTimer::elapsed() was implemented using
driverStartTime + time.elapsed() while the driver
was running, but time.elapsed already contains
driverStartTime so that was counted twice. This caused
repeating timers to fire immediately once they first
had fired, if the animation driver was started while
it was running.

Separate the two timers. Animation driver time restarts
from 0 every time it starts.

Change-Id: Icf5cd0381b121b2355d7c6ec3edd0997721cbcdf
Task-number: QTBUG-41198
Reviewed-by: Michael Brasser <michael.brasser@live.com>

src/corelib/animation/qabstractanimation.cpp

@@ -877,6 +877,7 @@ void QAnimationDriver::start()
     Q_D(QAnimationDriver);
     if (!d->running) {
         d->running = true;
+        d->timer.start();
         emit started();
     }
 }
@@ -900,9 +901,8 @@ void QAnimationDriver::stop()
 
 qint64 QAnimationDriver::elapsed() const
 {
-    // The default implementation picks up the elapsed time from the
-    // unified timer and can ignore the time offset.
-    return QUnifiedTimer::instance()->time.elapsed();
+    Q_D(const QAnimationDriver);
+    return d->running ? d->timer.elapsed() : 0;
 }
 
 /*!

src/corelib/animation/qabstractanimation_p.h

@@ -133,6 +133,7 @@ class Q_CORE_EXPORT QAnimationDriverPrivate : public QObjectPrivate
 {
 public:
     QAnimationDriverPrivate() : running(false) {}
+    QElapsedTimer timer;
     bool running;
 };