[Android] Fix return code for Sharded Perf step.

BUG=615157

Review-Url: https://codereview.chromium.org/2169093003
Cr-Original-Commit-Position: refs/heads/master@{#406970}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: bec4caf4bf87bdc03f93e5e27c8ab7c14370df8b

android/test_runner.py

@@ -933,6 +933,9 @@ def RunTestsInPlatformMode(args):
           json_results.GenerateJsonResultsFile(
               all_raw_results, args.json_results_file)
 
+  if args.command == 'perf' and (args.steps or args.single_step):
+    return 0
+
   return (0 if all(r.DidRunPass() for r in all_iteration_results)
           else constants.ERROR_EXIT_CODE)