chrome: Cleanup class/struct forward declarations

chrome/browser/metrics/chromeos_metrics_provider.h

 // Copyright 2014 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_CHROMEOS_METRICS_PROVIDER_H_
 #define CHROME_BROWSER_METRICS_CHROMEOS_METRICS_PROVIDER_H_
 
 #include <stdint.h>
 
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "chrome/browser/metrics/leak_detector/leak_detector_controller.h"
 #include "chrome/browser/metrics/perf/perf_provider_chromeos.h"
 #include "components/metrics/metrics_provider.h"
 
 namespace device {
 class BluetoothAdapter;
 }
 
 namespace metrics {
 class ChromeUserMetricsExtension;
 }
 
 class PrefRegistrySimple;
-class PrefService;
 
 // Performs ChromeOS specific metrics logging.
 class ChromeOSMetricsProvider : public metrics::MetricsProvider {
  public:
   // Possible device enrollment status for a Chrome OS device.
   // Used by UMA histogram, so entries shouldn't be reordered or removed.
   enum EnrollmentStatus {
     NON_MANAGED,
     UNUSED,  // Formerly MANAGED_EDU, see crbug.com/462770.
     MANAGED,
@@ skipping 74 matching lines @@
   // Hardware class (e.g., hardware qualification ID). This class identifies
   // the configured system components such as CPU, WiFi adapter, etc.
   std::string hardware_class_;
 
   base::WeakPtrFactory<ChromeOSMetricsProvider> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ChromeOSMetricsProvider);
 };
 
 #endif  // CHROME_BROWSER_METRICS_CHROMEOS_METRICS_PROVIDER_H_