Keep the old TimeToFirstScrollUpdateSwapBegin2 metrics until M56 is stable

content/browser/renderer_host/input/render_widget_host_latency_tracker.cc

 // 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.
 
 #include "content/browser/renderer_host/input/render_widget_host_latency_tracker.h"
 
 #include <stddef.h>
 
 #include "base/logging.h"
 #include "base/metrics/histogram_macros.h"
@@ skipping 243 matching lines @@
           latency_component_id, &original_component)) {
     scroll_name = "ScrollBegin";
     // This UMA metric tracks the time between the final frame swap for the
     // first scroll event in a sequence and the original timestamp of that
     // scroll event's underlying touch/wheel event.
 
     UMA_HISTOGRAM_TOUCH_WHEEL_TO_SCROLL_LATENCY(
         "Event.Latency.ScrollBegin." + event_type_name +
             ".TimeToScrollUpdateSwapBegin2",
         original_component, gpu_swap_begin_component);
+
+    // TODO(lanwei): Will remove them when M56 is stable, see
+    // https://crbug.com/669618.
+    UMA_HISTOGRAM_TOUCH_WHEEL_TO_SCROLL_LATENCY(
+        "Event.Latency.ScrollUpdate." + event_type_name +
+            ".TimeToFirstScrollUpdateSwapBegin2",
+        original_component, gpu_swap_begin_component);
   } else if (latency.FindLatency(
                  ui::INPUT_EVENT_LATENCY_SCROLL_UPDATE_ORIGINAL_COMPONENT,
                  latency_component_id, &original_component)) {
     // This UMA metric tracks the time from when the original touch event is
     // created to when the scroll gesture results in final frame swap.
     // First scroll events are excluded from this metric.
     if (event_type_name == "Touch") {
       UMA_HISTOGRAM_TOUCH_WHEEL_TO_SCROLL_LATENCY(
           "Event.Latency.ScrollUpdate." + event_type_name +
               ".TimeToScrollUpdateSwapBegin2",
@@ skipping 442 matching lines @@
   if (!latency.FindLatency(
           ui::INPUT_EVENT_LATENCY_GENERATE_SCROLL_UPDATE_FROM_MOUSE_WHEEL, 0,
           &mouse_wheel_scroll_update_component)) {
     ComputeScrollLatencyHistograms(
         gpu_swap_begin_component, gpu_swap_end_component, latency_component_id_,
         latency, is_running_navigation_hint_task);
   }
 }
 
 }  // namespace content