Update telemetry tests to be agnostic to ScrollTopLeftInterop mode

tools/telemetry/telemetry/internal/actions/scroll.py

 # Copyright 2012 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.internal.actions import page_action
 
 
 class ScrollAction(page_action.PageAction):
   # TODO(chrishenry): Ignore attributes, to be deleted when usage in
@@ skipping 60 matching lines @@
 
     done_callback = 'function() { window.__scrollActionDone = true; }'
     tab.ExecuteJavaScript("""
         window.__scrollActionDone = false;
         window.__scrollAction = new __ScrollAction(%s, %s);"""
         % (done_callback, self._distance_func))
 
   def RunAction(self, tab):
     if (self._selector is None and self._text is None and
         self._element_function is None):
-      self._element_function = 'document.body'
+      self._element_function = 'document.scrollingElement'
 
     gesture_source_type = self._synthetic_gesture_source
     if self._use_touch:
       gesture_source_type = 'chrome.gpuBenchmarking.TOUCH_INPUT'
 
     code = '''
         function(element, info) {
           if (!element) {
             throw Error('Cannot find element: ' + info);
           }
           window.__scrollAction.start({
             element: element,
             left_start_ratio: %s,
             top_start_ratio: %s,
             direction: '%s',
             speed: %s,
             gesture_source_type: %s
           });
         }''' % (self._left_start_ratio,
                 self._top_start_ratio,
                 self._direction,
                 self._speed,
                 gesture_source_type)
     page_action.EvaluateCallbackWithElement(
         tab, code, selector=self._selector, text=self._text,
         element_function=self._element_function)
     tab.WaitForJavaScriptExpression('window.__scrollActionDone', 60)