VideoOutput: Take the surface's viewport into account

Task-Number: QTBUG-30410

Change-Id: I480ce0bcd7ec136e54b5bfc5fec0e901141b72d8
Reviewed-by: Josh Faust <jfaust@suitabletech.com>
Reviewed-by: Yoann Lopes <yoann.lopes@digia.com>
qmlvideo example, add missing #ifdef PERFORMANCEMONITOR_SUPPORT

This usage of PerformanceMonitor needs to be protected by the same
preprocessor check as the header include that makes it available.

Change-Id: Ie8a1b6e99a61c333ceedcf2e9751235fc2efb415
Reviewed-by: Martin Smith <martin.smith@digia.com>