perf scripts python: exported-sql-viewer.py: Add LookupModel()

Add LookupModel() to find a model in the model cache without creating it.
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lore.kernel.org/lkml/20190821083216.1340-2-adrian.hunter@intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

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

@@ -341,6 +341,15 @@ def LookupCreateModel(model_name, create_fn):
 	model_cache_lock.release()
 	return model
 
+def LookupModel(model_name):
+	model_cache_lock.acquire()
+	try:
+		model = model_cache[model_name]
+	except:
+		model = None
+	model_cache_lock.release()
+	return model
+
 # Find bar
 
 class FindBar():