Add sharding support to browser_test_runner.

telemetry/examples/browser_tests/simple_sharding_test.py

+# Copyright 2016 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.
+
+from telemetry.testing import serially_executed_browser_test_case
+
+
+class SimpleShardingTest(
+    serially_executed_browser_test_case.SeriallyBrowserTestCase):
+
+  def Test1(self):
+    pass
+
+  def Test2(self):
+    pass
+
+  def Test3(self):
+    pass
+
+  @classmethod
+  def GenerateTestCases_PassingTest(cls, options):
+    del options  # unused
+    for i in xrange(10):
+      yield 'passing_test_' + str(i), (i,)
+
+  def PassingTest(self, a):
+    self.assertGreaterEqual(a, 0)