Use case: User is debugging a process instance. User would like to know what
code path has been executed for this process. Today the only thing which is
shown is the current activity. So user does not know at a glance what executed
before the current activity.

Proposal: Visually trace the flow of execution on the process diagram. 

Basic idea: When a particular process instance is being debugged, the diagram
will show all visited activities in their normal rendering. Unvisited activities
will be "greyed" out.  This will allow the user to trace the process execution. 

This fucntionality will overlap somewhat with that which will be provided by the
Process Execution View issue 81863. However, I believe both views are useful and
complimentary. The Process Execution View is better capable of showing the
history of looped structures. The Process diagram is better at showing the
current code path relative to the overall process. Both views are helpful and
desirable.

This will require more detail and description in a functional specification.