Add a LayoutNG version of the loading.{desktop,mobile} benchmarks

R=eae@chromium.org, kojii@chromium.org

Change-Id: I78bda450dd122b256495b33489dc8bfb7b39fb15
Reviewed-on: https://chromium-review.googlesource.com/1259125Reviewed-by: Emil A Eklund <eae@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Commit-Queue: Christian Biesinger <cbiesinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#596279}

tools/perf/contrib/blink_layoutng_perf/loading_layout_ng.py

+# Copyright 2018 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 benchmarks import loading
+from telemetry import benchmark
+
+# pylint: disable=protected-access
+@benchmark.Info(emails=['cbiesinger@chromium.org'],
+                documentation_url='https://bit.ly/loading-benchmarks')
+class LoadingDesktopLayoutNg(loading.LoadingDesktop):
+  """A benchmark that runs loading.desktop with the layoutng flag."""
+
+  def SetExtraBrowserOptions(self, options):
+    super(LoadingDesktopLayoutNg, self).SetExtraBrowserOptions(options)
+    options.AppendExtraBrowserArgs('--enable-blink-features=LayoutNG')
+
+  @classmethod
+  def Name(cls):
+    return 'loading.desktop_layout_ng'
+
+
+# pylint: disable=protected-access
+@benchmark.Info(emails=['cbiesinger@chromium.org'],
+                documentation_url='https://bit.ly/loading-benchmarks')
+class LoadingMobileLayoutNg(loading.LoadingDesktop):
+  """A benchmark that runs loading.mobile with the layoutng flag."""
+
+  def SetExtraBrowserOptions(self, options):
+    super(LoadingMobileLayoutNg, self).SetExtraBrowserOptions(options)
+    options.AppendExtraBrowserArgs('--enable-blink-features=LayoutNG')
+
+  @classmethod
+  def Name(cls):
+    return 'loading.mobile_layout_ng'