telemetry: add screenshot measurement

tools/perf/measurements/screenshot.py

+# Copyright 2014 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
+
+from telemetry.page import page_measurement
+from telemetry.page import page_test
+
+
+class Screenshot(page_measurement.PageMeasurement):
+  def __init__(self):
+    super(Screenshot, self).__init__(
+        action_name_to_run = 'RunPrepareForScreenshot',
+        is_action_name_to_run_optional=True)
+
+  @classmethod
+  def AddCommandLineArgs(cls, parser):
+    parser.add_option('--png-outdir',
+                      help='Output directory for the PNG files')
+
+  @classmethod
+  def ProcessCommandLineArgs(cls, parser, args):
+    if not args.png_outdir:
+      parser.error('Please specify --png-outdir')
+    cls._png_outdir = args.png_outdir
+
+  def MeasurePage(self, page, tab, results):
+    if not tab.screenshot_supported:
+      raise page_test.TestNotSupportedOnPlatformFailure(
+          'Browser does not support screenshotting')
+
+    tab.WaitForDocumentReadyStateToBeComplete()
+    screenshot = tab.Screenshot(60)
+
+    outpath = os.path.abspath(
+        os.path.join(self._png_outdir, page.file_safe_name)) + '.png'
+
+    if os.path.exists(outpath):
+      previous_mtime = os.path.getmtime(outpath)
+    else:
+      previous_mtime = -1
+
+    screenshot.WritePngFile(outpath)
+
+    saved_picture_count = 0
+    if os.path.exists(outpath) and os.path.getmtime(outpath) > previous_mtime:
+      saved_picture_count = 1
+    results.Add('saved_picture_count', 'count', saved_picture_count)