WIP: Plumbing input event latency reporting through Mus GPU.

ui/latency/latency_tracker.h

Index: ui/latency/latency_tracker.h
diff --git a/ui/latency/latency_tracker.h b/ui/latency/latency_tracker.h
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+// Copyright 2017 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 UI_LATENCY_LATENCY_TRACKER_H_
+#define UI_LATENCY_LATENCY_TRACKER_H_
+
+#include <stdint.h>
+
+#include <vector>
+
+#include "base/macros.h"
+#include "ui/latency/latency_info.h"
+
+namespace ui {
+
+// Utility class for tracking the latency of events.
+class LatencyTracker {
+ public:
+  LatencyTracker() = default;
+  ~LatencyTracker() = default;
+
+  // Terminates latency tracking for events that triggered rendering, also
+  // performing relevant UMA latency reporting.
+  // Called when GPU buffers swap completes.
+  void OnGpuSwapBuffersCompleted(const LatencyInfo& latency);
+
+ protected:
+  virtual void ReportRapporScrollLatency(
+      const std::string& name,
+      const LatencyInfo::LatencyComponent& start_component,
+      const LatencyInfo::LatencyComponent& end_component);
+
+ private:
+  void ComputeTouchAndWheelScrollLatencyHistograms(
+      const LatencyInfo::LatencyComponent& gpu_swap_begin_component,
+      const LatencyInfo::LatencyComponent& gpu_swap_end_component,
+      const LatencyInfo& latency);
+
+  DISALLOW_COPY_AND_ASSIGN(LatencyTracker);
+};
+
+}  // namespace latency
+
+#endif  // UI_LATENCY_LATENCY_TRACKER_H_