smoothness.scrolling_tough_ad_cases to use browser driven scrolls

tools/perf/page_sets/tough_ad_cases.py

Index: tools/perf/page_sets/tough_ad_cases.py
diff --git a/tools/perf/page_sets/tough_ad_cases.py b/tools/perf/page_sets/tough_ad_cases.py
index 75ba6e53ca0f40e8eba5222a21bcf764801c299c..a203d6efcbfb4fb558130254a672beb49e609e1e 100644
--- a/tools/perf/page_sets/tough_ad_cases.py
+++ b/tools/perf/page_sets/tough_ad_cases.py
@@ -4,6 +4,7 @@
 
 from telemetry.core import exceptions
 from telemetry.page import page as page_module
+from telemetry.web_perf import timeline_interaction_record
 from telemetry import story
 
 
@@ -59,13 +60,25 @@ class ScrollingPage(page_module.Page):
     action_runner.WaitForJavaScriptCondition('document.body !== null')
 
   def RunPageInteractions(self, action_runner):
-    for _ in range(10):
-      with action_runner.CreateGestureInteraction('ScrollAction',
-                                                  repeatable=True):
-        action_runner.ScrollPage(distance=500,
-                                 top_start_ratio=self._top_start_ratio)
-      action_runner.Wait(.25)
-
+    # Set up a browser driven repeating scroll.  The delay between the scrolls
+    # should be unaffected by render thread responsivness (or lack there of).
+    flags = [timeline_interaction_record.REPEATABLE]
+    scroll_command = {
+      'method': 'Input.synthesizeScrollGesture',
+      'params': {
+        'x': 500,

[Sami, 2015/08/17 17:06:44]

Can we compute these to always be the middle of screen? Otherwise this might be
flaky depending on the screen size.

[alex clarke (OOO till 29th), 2015/08/18 13:40:51]

Done.

+        'y': 500,
+        'xDistance': 0,
+        'yDistance': -300,
+        'preventFling': True,
+        'repeatCount': 9,

[Sami, 2015/08/17 17:06:44]

10 assuming we change repeatCount to mean the total number of gestures.

[alex clarke (OOO till 29th), 2015/08/18 13:40:51]

Acknowledged.

+        'repeatDelayMs': 250,
+        'interactionMarkerName':
+            timeline_interaction_record.GetJavaScriptMarker(
+                'Gesture_ScrollAction', flags),
+        }
+      }
+    action_runner.tab.RunInspectorCommand(scroll_command)
 
 class ScrollingForbesPage(ScrollingPage):