Implemented telemetry benchmark that loads page and outputs screenshot.

tools/perf/contrib/cluster_telemetry/screenshot_unittest.py

Index: tools/perf/contrib/cluster_telemetry/screenshot_unittest.py
diff --git a/tools/perf/contrib/cluster_telemetry/screenshot_unittest.py b/tools/perf/contrib/cluster_telemetry/screenshot_unittest.py
new file mode 100644
index 0000000000000000000000000000000000000000..4127343ab8be64f72a85be55f0db64515b53e8fe
--- /dev/null
+++ b/tools/perf/contrib/cluster_telemetry/screenshot_unittest.py
@@ -0,0 +1,36 @@
+# Copyright 2017 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 os
+import platform
+import shutil
+import tempfile
+
+from telemetry.testing import options_for_unittests
+from telemetry.testing import page_test_test_case
+from contrib.cluster_telemetry import screenshot
+
+class ScreenshotUnitTest(page_test_test_case.PageTestTestCase):
+
+  def setUp(self):
+    self._options = options_for_unittests.GetCopy()
+    self._png_outdir = tempfile.mkdtemp('_png_test')
+
+  def tearDown(self):
+    shutil.rmtree(self._png_outdir)
+
+  def testScreenshot(self):
+    # Screenshots for Cluster Telemetry purposes currently only supported on
+    # Linux platform.
+    if platform.system() != 'Linux':

[nednguyen, 2017/06/09 18:11:09]

You would want to do @decorators.Enabled('linux') instead. This will make the
test run if the platform is Android.

+      return
+
+    page_set = self.CreateStorySetFromFileInUnittestDataDir('blank.html')
+    measurement = screenshot.Screenshot(self._png_outdir)
+    self.RunMeasurement(measurement, page_set, options=self._options)
+
+    path = self._png_outdir + '/' + page_set.stories[0].file_safe_name + '.png'
+    self.assertTrue(os.path.exists(path))
+    self.assertTrue(os.path.isfile(path))
+    self.assertTrue(os.access(path, os.R_OK))

[nednguyen, 2017/06/09 18:11:09]

In general, test should not leave files around after they are finished.
We should clean up the png file path in a finally block:
try:
 ...
finally:
  remove directory that store png files

[lchoi, 2017/06/09 18:16:51]

I'm pretty sure the tearDown() fn above takes care of this. Just tried running a
test and locating the test directory and .png based on the log output and I
could not find them. But please correct me if I'm wrong!

[nednguyen, 2017/06/09 18:22:59]

Ah right. Sorry that i missed the tearDown