Setting --run-python-script flag for runtest.py invocation.

scripts/slave/recipe_modules/bisect_tester/perf_test.py

Index: scripts/slave/recipe_modules/bisect_tester/perf_test.py
diff --git a/scripts/slave/recipe_modules/bisect_tester/perf_test.py b/scripts/slave/recipe_modules/bisect_tester/perf_test.py
index 0c6f3147070eea41641f50a997cf0935d8a0308c..f6fd769579a16b8e0fb0a23570d6074f2a394568 100644
--- a/scripts/slave/recipe_modules/bisect_tester/perf_test.py
+++ b/scripts/slave/recipe_modules/bisect_tester/perf_test.py
@@ -199,12 +199,20 @@ def _run_command(api, command, step_name):
   if 'android-chrome' in command:  # pragma: no cover
     kwargs['env'] = {'CHROMIUM_OUTPUT_DIR': api.m.chromium.output_dir}
 
+  run_python_command = False
+  if command_parts[0].startswith('python'):  # pragma: no cover
+    # Handling case when dashboard sends python as the command (for windows).
+    command_parts = command_parts[1:]
+    run_python_command = True
+  elif _is_telemetry_command(command):
+    run_python_command = True

[sullivan, 2016/04/25 18:43:12]

The code could use some more comments explaining exactly what's going on:

1) We need this python_mode=True and need to strip 'python' out of the command
for runtest.py? Are more details available about why?

2) The dashboard sends 'python' as the command: why do we handle that case here
instead of change the dashboard?

3) Why do we check command_parts[0].startswith('python') and then drop the
entire thing if it does? Could it be anything other than 'python'? If it could,
what are we dropping?

4) Why do we effectively have two names for what appears to be telling
run_test.py to prepend 'python ' to the command (run_python_command and
python_mode)?

[RobertoCN, 2016/04/25 19:34:31]

Done.

   try:
     step_result = api.m.chromium.runtest(
         test=_rebase_path(command_parts[0]),
         args=command_parts[1:],
         xvfb=True,
         name=step_name,
+        python_mode=run_python_command,
         stdout=stdout,
         stderr=stderr,
         **kwargs)