[perfcompare] Add a placeholder "compare_perf" command for the recipe to invoke

This a placeholder entry point for the fuchsia_perfcompare.py recipe
to invoke.  I will add the actual perf results comparison logic in a
later change.

Bug: IN-646
Test: tested via 'led' with recipe change
Change-Id: Ieb18a9a2f9c9121a8a16f8fd0089589cd8f94d3b
diff --git a/garnet/bin/perfcompare/perfcompare.py b/garnet/bin/perfcompare/perfcompare.py
index 9133eb8..71ff44d 100644
--- a/garnet/bin/perfcompare/perfcompare.py
+++ b/garnet/bin/perfcompare/perfcompare.py
@@ -8,25 +8,27 @@
 
 import argparse
 import json
+import os
 import sys
 
 
+def ComparePerf(args):
+    # This code is just a placeholder to allow the infra recipe to be
+    # tested easily.  It does not compare the performance test results yet.
+    # It just prints the filenames of the perf test result files.
+    for dir_path in [args.results_dir_before, args.results_dir_after]:
+        print '\n-- in directory %r:' % dir_path
+        for filename in sorted(os.listdir(dir_path)):
+            print filename
+
+
 def TotalSize(snapshot_file):
     with open(snapshot_file) as fh:
         data = json.load(fh)
     return sum(info['size'] for info in data['blobs'].itervalues())
 
 
-def Main(argv):
-    parser = argparse.ArgumentParser()
-    subparsers = parser.add_subparsers()
-    parser_compare = subparsers.add_parser(
-        'compare_sizes',
-        help='Compare file sizes specified by two system.snapshot files')
-    parser_compare.add_argument('snapshot_before')
-    parser_compare.add_argument('snapshot_after')
-    args = parser.parse_args(argv)
-
+def CompareSizes(args):
     filenames = [args.snapshot_before, args.snapshot_after]
     sizes = [TotalSize(filename) for filename in filenames]
     print 'Size before:  %d bytes' % sizes[0]
@@ -36,5 +38,27 @@
         print 'Factor of:    %f' % (float(sizes[1]) / sizes[0])
 
 
+def Main(argv):
+    parser = argparse.ArgumentParser()
+    subparsers = parser.add_subparsers()
+
+    parser_compare_perf = subparsers.add_parser(
+        'compare_perf',
+        help='Compare two sets of perf test results')
+    parser_compare_perf.add_argument('results_dir_before')
+    parser_compare_perf.add_argument('results_dir_after')
+    parser_compare_perf.set_defaults(func=ComparePerf)
+
+    parser_compare_sizes = subparsers.add_parser(
+        'compare_sizes',
+        help='Compare file sizes specified by two system.snapshot files')
+    parser_compare_sizes.add_argument('snapshot_before')
+    parser_compare_sizes.add_argument('snapshot_after')
+    parser_compare_sizes.set_defaults(func=CompareSizes)
+
+    args = parser.parse_args(argv)
+    args.func(args)
+
+
 if __name__ == '__main__':
     Main(sys.argv[1:])