[Sync] Replace typedef with using.

components/sync/device_info/device_count_metrics_provider.h

 // 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 "base/macros.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:
-  typedef base::Callback<void(std::vector<const DeviceInfoTracker*>* trackers)>
-      ProvideTrackersCallback;
+  using ProvideTrackersCallback =
+      base::Callback<void(std::vector<const DeviceInfoTracker*>* trackers)>;
 
   explicit DeviceCountMetricsProvider(
       const ProvideTrackersCallback& provide_trackers);
   ~DeviceCountMetricsProvider() override;
 
   // MetricsProvider:
   void ProvideGeneralMetrics(
       metrics::ChromeUserMetricsExtension* uma_proto) override;
 
  private:
   // Returns the max number of active devices across all accounts.
   int MaxActiveDeviceCount() const;
 
   const ProvideTrackersCallback provide_trackers_;
 
   DISALLOW_COPY_AND_ASSIGN(DeviceCountMetricsProvider);
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_DEVICE_INFO_DEVICE_COUNT_METRICS_PROVIDER_H_