smoothness.scrolling_tough_ad_cases to use browser driven scrolls

tools/telemetry/telemetry/internal/backends/chrome_inspector/inspector_backend.py

Index: tools/telemetry/telemetry/internal/backends/chrome_inspector/inspector_backend.py
diff --git a/tools/telemetry/telemetry/internal/backends/chrome_inspector/inspector_backend.py b/tools/telemetry/telemetry/internal/backends/chrome_inspector/inspector_backend.py
index 3aa050a1f6f31bf9186167fe66fbde5f5e373fc5..3a79c2cd2dcc233d873e6295547adbb3d6f4cc86 100644
--- a/tools/telemetry/telemetry/internal/backends/chrome_inspector/inspector_backend.py
+++ b/tools/telemetry/telemetry/internal/backends/chrome_inspector/inspector_backend.py
@@ -223,6 +223,24 @@ class InspectorBackend(object):
     """
     return self._runtime.EnableAllContexts()
 
+  @_HandleInspectorWebSocketExceptions
+  def SynthesizeScrollGesture(self, params, timeout=60):
+    """Runs an inspector command to perform a browser driven scroll.
+
+    Args:
+      params: A dictionary containing Input.synthesizeScrollGesture arguments.
+
+    Raises:
+      exceptions.WebSocketDisconnected
+      exceptions.TimeoutException
+      exceptions.DevtoolsTargetCrashException
+    """
+    scroll_command = {
+      'method': 'Input.synthesizeScrollGesture',
+      'params': params
+    }
+    return self._runtime.RunInspectorCommand(scroll_command, timeout)
+
   # Timeline public methods.
 
   @property