perf scripts python: exported-sql-viewer.py: Add tree level

As preparation for adding support for copying to clipboard, keep track of
what level each item is in tree items.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/r/20190503120828.25326-4-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/scripts/python/exported-sql-viewer.py

@@ -456,6 +456,10 @@ class CallGraphLevelItemBase(object):
 		self.query_done = False;
 		self.child_count = 0
 		self.child_items = []
+		if parent_item:
+			self.level = parent_item.level + 1
+		else:
+			self.level = 0
 
 	def getChildItem(self, row):
 		return self.child_items[row]