Make changes to support bisect for android-chrome.

tools/auto_bisect/bisect_perf_regression_test.py

Index: tools/auto_bisect/bisect_perf_regression_test.py
diff --git a/tools/auto_bisect/bisect_perf_regression_test.py b/tools/auto_bisect/bisect_perf_regression_test.py
index c28c066da3cab0614beb7d9e843c2b99921694d4..df5f279baa3f3e8a8379b0f2c62c29edd82704ae 100644
--- a/tools/auto_bisect/bisect_perf_regression_test.py
+++ b/tools/auto_bisect/bisect_perf_regression_test.py
@@ -404,6 +404,14 @@ class BisectPerfRegressionTest(unittest.TestCase):
     self.assertEqual(
         181660, source_control.GetCommitPosition(wk_rev, depot_path))
 
+  def testGetCommitPositionForSkia(self):
+    bisect_instance = _GetBisectPerformanceMetricsInstance(DEFAULT_OPTIONS)
+    skia_rev = 'a94d028e0f2c77f159b3dac95eb90c3b4cf48c61'
+    depot_path = os.path.join(bisect_instance.src_cwd, 'third_party', 'skia')
+    # Skia doesn't use commit positions, and GetCommitPosition should
+    # return None for repos that don't use commit positions.
+    self.assertIsNone(source_control.GetCommitPosition(skia_rev, depot_path))
+
   def testUpdateDepsContent(self):
     bisect_instance = _GetBisectPerformanceMetricsInstance(DEFAULT_OPTIONS)
     deps_file = 'DEPS'