Fix reporting of TouchToFirstScroll latency metrics

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.h"
@@ skipping 409 matching lines @@
   DCHECK(latencies);
   for (LatencyInfo& latency : *latencies) {
     AddLatencyInfoComponentIds(&latency, latency_component_id_);
     latency.AddLatencyNumber(
         ui::INPUT_EVENT_BROWSER_RECEIVED_RENDERER_SWAP_COMPONENT, 0, 0);
   }
 }
 
 void RenderWidgetHostLatencyTracker::OnFrameSwapped(
     const LatencyInfo& latency) {
+  // Don't report frame latency on wheel events. Previously they were only
+  // reported on Touch metrics and we need to be consistent across reporting

[tdresser, 2016/04/22 17:55:59]

nit: inconsistent capitalization.

Might as well "Touch" -> "touch"

[dtapuska, 2016/04/22 18:14:59]

Done.

+  // metrics.
+  LatencyInfo::LatencyComponent mouse_wheel_scroll_update_component;
+  if (latency.FindLatency(
+          ui::INPUT_EVENT_LATENCY_GENERATE_SCROLL_UPDATE_FROM_MOUSE_WHEEL, 0,
+          &mouse_wheel_scroll_update_component)) {
+    return;
+  }
+
   LatencyInfo::LatencyComponent gpu_swap_end_component;
   if (!latency.FindLatency(
           ui::INPUT_EVENT_LATENCY_TERMINATED_FRAME_SWAP_COMPONENT, 0,
           &gpu_swap_end_component)) {
     return;
   }
 
   LatencyInfo::LatencyComponent gpu_swap_begin_component;
   if (!latency.FindLatency(ui::INPUT_EVENT_GPU_SWAP_BUFFER_COMPONENT, 0,
                            &gpu_swap_begin_component)) {
@@ skipping 14 matching lines @@
                            latency_component_id_, nullptr)) {
     return;
   }
 
   ComputeScrollLatencyHistograms(gpu_swap_begin_component,
                                  gpu_swap_end_component, latency_component_id_,
                                  latency);
 }
 
 }  // namespace content