chrome: Cleanup class/struct forward declarations

chrome/browser/metrics/metrics_reporting_state.h

 // Copyright (c) 2011 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 CHROME_BROWSER_METRICS_METRICS_REPORTING_STATE_H_
 #define CHROME_BROWSER_METRICS_METRICS_REPORTING_STATE_H_
 
 #include "base/callback.h"
 #include "components/metrics/metrics_service_client.h"
 
 typedef base::Callback<void(bool)> OnMetricsReportingCallbackType;
 
-class PrefService;
-class PrefRegistrySimple;
-
 // Changes metrics reporting state without caring about the success of the
 // change.
 void ChangeMetricsReportingState(bool enabled);
 
 // Changes metrics reporting state to the new value of |enabled|. Starts or
 // stops the metrics service based on the new state and then runs |callback_fn|
 // (which can be null) with the updated state (as the operation may fail). On
 // platforms other than CrOS and Android, also updates the underlying pref.
 // TODO(gayane): Support setting the pref on all platforms.
 void ChangeMetricsReportingStateWithReply(
     bool enabled,
     const OnMetricsReportingCallbackType& callback_fn);
 
 // Update metrics prefs on a permission (opt-in/out) change. When opting out,
 // this clears various client ids. When opting in, this resets saving crash
 // prefs, so as not to trigger upload of various stale data.
 void UpdateMetricsPrefsOnPermissionChange(bool metrics_enabled);
 
 // Returns whether MetricsReporting can be modified by the user (except
 // Android).
 bool IsMetricsReportingPolicyManaged();
 
 // Initialize kMetricsReportingEnabled based on kStatsReportingPref device
 // setting and add an observer as it is the source of truth on Chrome OS.
 void SetupMetricsStateForChromeOS();
 
 #endif  // CHROME_BROWSER_METRICS_METRICS_REPORTING_STATE_H_