Adds a LAST_NON_NULL window function to the trace processor.
Adds a LAST_NON_NULL window function to the trace processor.

The LAST_NON_NULL window function returns the last non-null value of its
expression within the window, or NULL if none has been encountered.

Change-Id: Ibfed136dea2e272031ba2616e5dcf4b8dc6bd20c

google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto