Implemented telemetry benchmark that loads page and outputs screenshot.

tools/perf/contrib/cluster_telemetry/screenshot_unittest.py

+# 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):
+    page_set = self.CreateStorySetFromFileInUnittestDataDir('blank.html')
+    measurement = screenshot.Screenshot(self._png_outdir)
+    results = self.RunMeasurement(measurement, page_set, options=self._options)
+
+    # Screenshots not supported if failure occurs on Linux
+    if results.failures and platform.system() == 'Linux':

[wkorman, 2017/06/08 23:14:41]

Don't we want the inverse? If it's Linux, we want to make sure they *are*
supported?

+      assert 'not supported' in results.failures[0].exc_info[1].message
+      return
+
+    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))