Add latency metric mean_js_touch_scroll_latency for JS touch handler driven scroll

tools/perf/metrics/smoothness.py

 # Copyright 2013 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 metrics import Metric
 from metrics import rendering_stats
 from metrics import statistics
 from telemetry.page import page_measurement
 from telemetry.page.perf_tests_helper import FlattenList
 
@@ skipping 74 matching lines @@
       results.Add('mean_mouse_wheel_scroll_latency', 'ms',
                   round(mean_mouse_wheel_scroll_latency, 3))
 
     if self._stats.touch_scroll_latency:
       mean_touch_scroll_latency = statistics.ArithmeticMean(
           self._stats.touch_scroll_latency,
           len(self._stats.touch_scroll_latency))
       results.Add('mean_touch_scroll_latency', 'ms',
                   round(mean_touch_scroll_latency, 3))
 
+    if self._stats.js_touch_scroll_latency:
+      mean_js_touch_scroll_latency = statistics.ArithmeticMean(
+          self._stats.js_touch_scroll_latency,
+          len(self._stats.js_touch_scroll_latency))
+      results.Add('mean_js_touch_scroll_latency', 'ms',
+                  round(mean_js_touch_scroll_latency, 3))
+
     # List of raw frame times.
     frame_times = FlattenList(self._stats.frame_times)
     results.Add('frame_times', 'ms', frame_times)
 
     # Arithmetic mean of frame times.
     mean_frame_time = statistics.ArithmeticMean(frame_times,
                                                 len(frame_times))
     results.Add('mean_frame_time', 'ms', round(mean_frame_time, 3))
 
     # Absolute discrepancy of frame time stamps.
     jank = statistics.FrameDiscrepancy(self._stats.frame_timestamps)
     results.Add('jank', '', round(jank, 4))
 
     # Are we hitting 60 fps for 95 percent of all frames?
     # We use 19ms as a somewhat looser threshold, instead of 1000.0/60.0.
     percentile_95 = statistics.Percentile(frame_times, 95.0)
     results.Add('mostly_smooth', 'score', 1.0 if percentile_95 < 19.0 else 0.0)
 
     if tab.browser.platform.IsRawDisplayFrameRateSupported():
       for r in tab.browser.platform.GetRawDisplayFrameRateMeasurements():
         if r.value is None:
           raise MissingDisplayFrameRateError(r.name)
         results.Add(r.name, r.unit, r.value)