Change Android retry logic - always retry 3 times.

build/android/pylib/base/base_test_sharder.py

 # Copyright (c) 2012 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.
 
 
 import logging
 import multiprocessing
 
 from pylib import android_commands
 from pylib.base.test_result import TestResults
 from pylib.forwarder import Forwarder
 
 
+# Number of times we retry a test suite in case of failure.
+NUM_RETRIES = 3
+
+
 def _ShardedTestRunnable(test):
   """Standalone function needed by multiprocessing.Pool."""
   log_format = '[' + test.device + '] # %(asctime)-15s: %(message)s'
   if logging.getLogger().handlers:
     logging.getLogger().handlers[0].setFormatter(logging.Formatter(log_format))
   else:
     logging.basicConfig(format=log_format)
   # Handle SystemExit here since python has a bug to exit current process
   try:
     return test.Run()
@@ skipping 23 matching lines @@
     self.attached_devices = attached_devices
     # Worst case scenario: a device will drop offline per run, so we need
     # to retry until we're out of devices.
 
     # TODO(frankf): There are two sources of flakiness:
     # 1. Device flakiness
     # 2. Test/product flakiness
     # We should differentiate between these. Otherwise, blindly retrying tests
     # might mask test/product flakiness. For type 2, we should follow the
     # general chrome best practices.
-    self.retries = len(self.attached_devices)
+    self.retries = NUM_RETRIES
     self.tests = []
     self.build_type = build_type
 
   def CreateShardedTestRunner(self, device, index):
     """Factory function to create a suite-specific test runner.
 
     Args:
       device: Device serial where this shard will run
       index: Index of this device in the pool.
 
@@ skipping 79 matching lines @@
         for t in test_results.GetAllBroken():
           self.tests += [t.name]
         if not self.tests:
           break
     else:
       # We ran out retries, possibly out of healthy devices.
       # There's no recovery at this point.
       raise Exception('Unrecoverable error while retrying test runs.')
     self._KillHostForwarder()
     return final_results