[Android] Fix error in sharding of gtests.

build/android/run_tests.py

 #!/usr/bin/env python
 #
 # 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.
 
 """Runs all the native unit tests.
 
 1. Copy over test binary to /data/local on device.
 2. Resources: chrome/unit_tests requires resources (chrome.pak and en-US.pak)
@@ skipping 158 matching lines @@
     """Creates a suite-specific test runner.
 
     Args:
       device: Device serial where this shard will run.
       index: Index of this device in the pool.
 
     Returns:
       A SingleTestRunner object.
     """
     device_num = len(self.attached_devices)
-    shard_size = (len(self.tests) + device_num - 1) / device_num
-    shard_test_list = self.tests[index * shard_size : (index + 1) * shard_size]
+    shard_test_list = self.tests[index::device_num]
     test_filter = ':'.join(shard_test_list) + self.gtest_filter
     return SingleTestRunner(
         device,
         self.test_suite,
         test_filter,
         self.test_arguments,
         self.timeout,
         self.cleanup_test_files, self.tool, index,
         not not self.log_dump_name,
         self.build_type,
@@ skipping 142 matching lines @@
   # the batch (this happens because the exit status is a sum of all failures
   # from all suites, but the buildbot associates the exit status only with the
   # most recent step).
   if options.exit_code:
     return failed_tests_count
   return 0
 
 
 if __name__ == '__main__':
   sys.exit(main(sys.argv))