text: // Copyright 2016 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 COMPONENTS_SYNC_DEVICE_INFO_DEVICE_COUNT_METRICS_PROVIDER_H_
  #define COMPONENTS_SYNC_DEVICE_INFO_DEVICE_COUNT_METRICS_PROVIDER_H_
  
  #include <memory>
  #include <vector>
  
  #include "base/callback.h"
  #include "components/metrics/metrics_provider.h"
  
  namespace syncer {
  
  class DeviceInfoTracker;
  
  // A registerable metrics provider that will emit the number of active syncing
  // devices a user has upon UMA upload. When there are multiple active profiles
  // that are aware of syncable devices, the largest count is used. This approach
  // is useful for several reasons. We're significantly interested in "power"
  // users that have multiple devices and profiles, and if we skipped emitting any
  // metrics in multi profile cases, then we'd be unaware of this entire segment
  // of the population. If we emitted multiple metrics, we would have much more
  // noise and discerning which metrics actually belonged to non-syncing users
  // would be much trickier.
  class DeviceCountMetricsProvider : public metrics::MetricsProvider {
   public:
    using ProvideTrackersCallback = base::RepeatingCallback<void(
        std::vector<const DeviceInfoTracker*>* trackers)>;
  
    explicit DeviceCountMetricsProvider(
        const ProvideTrackersCallback& provide_trackers);
  
    DeviceCountMetricsProvider(const DeviceCountMetricsProvider&) = delete;
    DeviceCountMetricsProvider& operator=(const DeviceCountMetricsProvider&) =
        delete;
  
    ~DeviceCountMetricsProvider() override;
  
    // MetricsProvider:
    void ProvideCurrentSessionData(
        metrics::ChromeUserMetricsExtension* uma_proto) override;
  
   private:
    // Returns the max number of active devices across all accounts.
    int MaxActiveDeviceCount() const;
  
    const ProvideTrackersCallback provide_trackers_;
  };
  
  }  // namespace syncer
  
  #endif  // COMPONENTS_SYNC_DEVICE_INFO_DEVICE_COUNT_METRICS_PROVIDER_H_
  