as_pandas() -> as_pandas_dataframe(); add __str__ representation

Change-Id: I357f9544572fd93bd4a50a9b11f05aaa38121964

src/trace_processor/python/example.py

diff --git a/src/trace_processor/python/example.py b/src/trace_processor/python/example.py
index 5788aa3..b3925a4 100644
--- a/src/trace_processor/python/example.py
+++ b/src/trace_processor/python/example.py
@@ -46,14 +46,14 @@
         addr=args.address, file_path=args.file, bin_path=args.binary)
 
   # Iterate through QueryResultIterator
-  res_it = tp.query('select name from slice')
+  res_it = tp.query('select * from slice limit 10')
   for row in res_it:
     print(row.name)
 
   # Convert QueryResultIterator into a pandas dataframe + iterate. This yields
   # the same results as the function above.
   try:
-    res_df = tp.query('select name from slice').as_pandas()
+    res_df = tp.query('select * from slice limit 10').as_pandas_dataframe()
     for index, row in res_df.iterrows():
       print(row['name'])
   except Exception: