Aggregate non-shader GPU operations into their own operations

Aggregate non-shader GPU operations into their own operations

These operations are named after representative functions, (glClear,
glReadPixels, etc.). Aggregate time spent in any of these operations
is sorted together with the existing reports for time spent in
particular shader programs.

The shader program times should now be more accurate since time spent
in operations such as glClear will now no longer be accumulated into
the most recently-used shader.