Add a sampling scheme to ScrollUpdate.Touch UKM

content/browser/renderer_host/input/render_widget_host_latency_tracker.h

 // 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.
 
 #ifndef CONTENT_BROWSER_RENDERER_HOST_INPUT_RENDER_WIDGET_HOST_LATENCY_TRACKER_H_
 #define CONTENT_BROWSER_RENDERER_HOST_INPUT_RENDER_WIDGET_HOST_LATENCY_TRACKER_H_
 
 #include <stdint.h>
 
 #include <vector>
 
 #include "base/macros.h"
 #include "content/browser/renderer_host/event_with_latency_info.h"
 #include "content/common/content_export.h"
 #include "content/common/input/input_event_ack_state.h"
 #include "services/metrics/public/cpp/ukm_recorder.h"
 #include "ui/latency/latency_info.h"
 #include "ui/latency/latency_tracker.h"
 
 namespace content {
 
 class RenderWidgetHostDelegate;
 
 // Utility class for tracking the latency of events passing through
 // a given RenderWidgetHost.
 class CONTENT_EXPORT RenderWidgetHostLatencyTracker
     : NON_EXPORTED_BASE(public ui::LatencyTracker) {
  public:
-  explicit RenderWidgetHostLatencyTracker();
+  explicit RenderWidgetHostLatencyTracker(bool metric_sampling);
   ~RenderWidgetHostLatencyTracker();
 
   // Associates the latency tracker with a given route and process.
   // Called once after the RenderWidgetHost is fully initialized.
   void Initialize(int routing_id, int process_id);
 
   void ComputeInputLatencyHistograms(blink::WebInputEvent::Type type,
                                      int64_t latency_component_id,
                                      const ui::LatencyInfo& latency,
                                      InputEventAckState ack_result);
@@ skipping 52 matching lines @@
   int64_t latency_component_id_;
   float device_scale_factor_;
   bool has_seen_first_gesture_scroll_update_;
   // Whether the current stream of touch events includes more than one active
   // touch point. This is set in OnInputEvent, and cleared in OnInputEventAck.
   bool active_multi_finger_gesture_;
   // Whether the touch start for the current stream of touch events had its
   // default action prevented. Only valid for single finger gestures.
   bool touch_start_default_prevented_;
 
+  // Whether the sampling is needed for high volume metrics. This will be off
+  // when we are in unit tests. This is a temporary field so we can come up with
+  // a more permanent solution for crbug.com/739169.
+  bool metric_sampling_;
+  int metric_sampling_events_since_last_sample_;
+
   RenderWidgetHostDelegate* render_widget_host_delegate_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderWidgetHostLatencyTracker);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_INPUT_RENDER_WIDGET_HOST_LATENCY_TRACKER_H_