Add scrolling power test.

tools/perf/page_sets/trivial_sites.py

+# Copyright 2016 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 telemetry.page import page as page_module
+from telemetry import story
+
+
+class TrivialScrollingPage(page_module.Page):
+
+  def __init__(self, page_set):
+    super(TrivialScrollingPage, self).__init__(
+        url='file://trivial_sites/trivial_scrolling_page.html',
+        page_set=page_set)
+
+
+class TrivialScrollStorySet(story.StorySet):
+
+  def __init__(self):
+    super(TrivialScrollStorySet, self).__init__()
+    self.AddStory(TrivialScrollingPage(self))