Fix confidence check and problems with successive builds due to symlinks.

tools/auto_bisect/bisect_perf_regression.py

 #!/usr/bin/env python
 # Copyright 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Chromium auto-bisect tool
 
 This script bisects a range of commits using binary search. It starts by getting
 reference values for the specified "good" and "bad" commits. Then, for revisions
 in between, it will get builds, run tests and classify intermediate revisions as
@@ skipping 485 matching lines @@
   error = False
   # Adding good and bad values to a parameter list.
   confidence_params = []
   for l in [known_bad_value['values'], known_good_value['values']]:
     # Flatten if needed, by averaging the values in each nested list
     if isinstance(l, list) and all([isinstance(x, list) for x in l]):
       averages = map(math_utils.Mean, l)
       confidence_params.append(averages)
     else:
       confidence_params.append(l)
-  regression_confidence = BisectResults.ConfidenceScore(*confidence_params)
+  regression_confidence = BisectResults.ConfidenceScore(
+      *confidence_params, accept_single_bad_or_good=True)
   if regression_confidence < REGRESSION_CONFIDENCE:
     error = REGRESSION_CONFIDENCE_ERROR_TEMPLATE.format(
         good_rev=good_revision,
         good_mean=known_good_value['mean'],
         good_std_err=known_good_value['std_err'],
         good_sample_size=len(known_good_value['values']),
         bad_rev=bad_revision,
         bad_mean=known_bad_value['mean'],
         bad_std_err=known_bad_value['std_err'],
         bad_sample_size=len(known_bad_value['values']))
@@ skipping 694 matching lines @@
     return build_success
 
   def RunGClientHooks(self):
     """Runs gclient with runhooks command.
 
     Returns:
       True if gclient reports no errors.
     """
     if self.opts.debug_ignore_build:
       return True
+    # Some "runhooks" calls create symlinks that other (older?) versions
+    # do not handle correctly causing the build to fail.  We want to avoid
+    # clearing the entire out/ directory so that changes close together will
+    # build faster so we just clear out all symlinks on the expectation that
+    # the next "runhooks" call will recreate everything properly.  Ignore
+    # failures (like Windows that doesn't have "find").
+    try:
+      bisect_utils.RunProcess(
+          ['find', 'out/', '-type', 'l', '-exec', 'rm', '-f', '{}', ';'],
+          cwd=self.src_cwd, shell=False)
+    except OSError:
+      pass
     return not bisect_utils.RunGClient(['runhooks'], cwd=self.src_cwd)
 
   def _IsBisectModeUsingMetric(self):
     return self.opts.bisect_mode in [bisect_utils.BISECT_MODE_MEAN,
                                      bisect_utils.BISECT_MODE_STD_DEV]
 
   def _IsBisectModeReturnCode(self):
     return self.opts.bisect_mode in [bisect_utils.BISECT_MODE_RETURN_CODE]
 
   def _IsBisectModeStandardDeviation(self):
@@ skipping 1648 matching lines @@
       # bugs. If you change this, please update the perf dashboard as well.
       bisect_utils.OutputAnnotationStepStart('Results')
     print 'Runtime Error: %s' % e
     if opts.output_buildbot_annotations:
       bisect_utils.OutputAnnotationStepClosed()
   return 1
 
 
 if __name__ == '__main__':
   sys.exit(main())