QmlProfiler's timeline has no more scroll bar if content is to big

Steps to reproduce:

• load a Qt Quick app or UI which produces some more events while executing (or make the profiler widget smaller)
• start profiling the application
• unfold some categories

Current result:

• lower categories can be reached when making the profiler widget big enough that they're displayed as well because of a missing scroll bar

Expected result:

• if timeline's content exceeds the height of the given widget a scroll bar should appear (as it was before switching to Quick 2)