[EasyUnlock] Move DataWithTimestamp out of ForegroundEidGenerator so it can be shared.

components/cryptauth/background_eid_generator.h

 // 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 COMPONENTS_CRYPTAUTH_BLE_BACKGROUND_EID_GENERATOR_H_
 #define COMPONENTS_CRYPTAUTH_BLE_BACKGROUND_EID_GENERATOR_H_
 
 #include <memory>
 #include <string>
 #include <vector>
 
 #include "base/macros.h"
 #include "base/time/clock.h"
+#include "components/cryptauth/data_with_timestamp.h"
 
 namespace cryptauth {
 
 class BeaconSeed;
 class RawEidGenerator;
 
 // Generates ephemeral ID (EID) values that are broadcast for background BLE
 // advertisements in the ProximityAuth protocol.
 //
 // When advertising in background mode, we offload advertising to the hardware
 // in order to conserve battery. We assume, however, that the scanning side is
 // not bound by battery constraints.
 //
 // For the inverse of this model, in which advertising is battery-sensitive, see
 // ForegroundEidGenerator.
 class BackgroundEidGenerator {
  public:
   BackgroundEidGenerator();
   virtual ~BackgroundEidGenerator();
 
   // Returns a list of the nearest EIDs from the current time. Note that the
   // list of EIDs is sorted from earliest timestamp to latest.
-  virtual std::vector<std::string> GenerateNearestEids(
+  virtual std::vector<DataWithTimestamp> GenerateNearestEids(
       const std::vector<BeaconSeed>& beacon_seed) const;
 
  private:
   friend class CryptAuthBackgroundEidGeneratorTest;
   BackgroundEidGenerator(std::unique_ptr<RawEidGenerator> raw_eid_generator,
                          std::unique_ptr<base::Clock> clock);
 
   // Helper function to generate the EID for any |timestamp_ms|, properly
   // calculating the start of the period. Returns nullptr if |timestamp_ms| is
   // outside of range of |beacon_seeds|.
-  std::unique_ptr<std::string> GenerateEid(
+  std::unique_ptr<DataWithTimestamp> GenerateEid(
       int64_t timestamp_ms,
       const std::vector<BeaconSeed>& beacon_seeds) const;
 
   std::unique_ptr<RawEidGenerator> raw_eid_generator_;
   std::unique_ptr<base::Clock> clock_;
 
   DISALLOW_COPY_AND_ASSIGN(BackgroundEidGenerator);
 };
 
 }  // cryptauth
 
 #endif  // COMPONENTS_CRYPTAUTH_BLE_BACKGROUND_EID_GENERATOR_H_