Turn off root scroller intervention on key_silk_cases page.

tools/perf/page_sets/key_silk_cases.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.
 from telemetry.page import page as page_module
 from telemetry.page import shared_page_state
 from telemetry import story
 
 
 class KeySilkCasesPage(page_module.Page):
 
@@ skipping 542 matching lines @@
       url='http://s.codepen.io/befamous/fullpage/pFsqb?scroll',
       page_set=page_set, run_no_page_interactions=run_no_page_interactions)
 
   def RunNavigateSteps(self, action_runner):
     super(Page26, self).RunNavigateSteps(action_runner)
     action_runner.WaitForJavaScriptCondition(
         'document.getElementsByClassName("tweet").length > 0')
     action_runner.Wait(1)
 
   def PerformPageInteractions(self, action_runner):
+    # Add a touch-action: none because this page prevent defaults all
+    # touch moves.
+    action_runner.ExecuteJavaScript('''
+        var style = document.createElement("style");
+        document.head.appendChild(style);
+        style.sheet.insertRule("body { touch-action: none }", 0);
+        ''')
     with action_runner.CreateGestureInteraction('ScrollAction'):
       action_runner.ScrollPage(distance=5000)
 
 
 class SVGIconRaster(KeySilkCasesPage):
 
   """ Why: Mutating SVG icons; these paint storm and paint slowly. """
 
   def __init__(self, page_set, run_no_page_interactions):
     super(SVGIconRaster, self).__init__(
@@ skipping 175 matching lines @@
     self.AddStory(SilkFinance(self, run_no_page_interactions))
     # Flaky interaction steps on Android; crbug.com/507865
     # self.AddStory(PolymerTopeka(self, run_no_page_interactions))
     self.AddStory(Masonry(self, run_no_page_interactions))
 
     for page in self:
       assert (page.__class__.RunPageInteractions ==
               KeySilkCasesPage.RunPageInteractions), (
               'Pages in this page set must not override KeySilkCasesPage\' '
               'RunPageInteractions method.')