Timestamps during tracing

[Eugene Velesevich]

As we have previously mentioned, we have worked on resurrecting timestamping
calls during tracing, and we would like to submit patches.  As I understand,
storing CPU timestamps as call details is a hard requirement.

Our main concern is what do to on the QApitrace side.  To visualize timing
data present in the trace, we have added two timeline panes to the main
QApitrace window (for CPU and GPU timestamps).  This is quite different from
the timeline visualization implemented for profiling during retracing, where
QApitrace opens a new window with multiple sub-timelines for different active
shader programs.

Would that be acceptable?