chrome: Cleanup class/struct forward declarations

chrome/browser/metrics/subprocess_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 CHROME_BROWSER_METRICS_SUBPROCESS_METRICS_PROVIDER_H_
 #define CHROME_BROWSER_METRICS_SUBPROCESS_METRICS_PROVIDER_H_
 
 #include <memory>
 #include <set>
 
 #include "base/gtest_prod_util.h"
 #include "base/id_map.h"
 #include "base/memory/weak_ptr.h"
 #include "base/scoped_observer.h"
 #include "base/threading/thread_checker.h"
 #include "components/metrics/metrics_provider.h"
 #include "content/public/browser/browser_child_process_observer.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 #include "content/public/browser/render_process_host_observer.h"
 
 namespace base {
 class PersistentHistogramAllocator;
-class SharedPersistentMemoryAllocator;
 }
 
 // SubprocessMetricsProvider gathers and merges histograms stored in shared
 // memory segments between processes. Merging occurs when a process exits,
 // when metrics are being collected for upload, or when something else needs
 // combined metrics (such as the chrome://histograms page).
 class SubprocessMetricsProvider : public metrics::MetricsProvider,
                                   public content::BrowserChildProcessObserver,
                                   public content::NotificationObserver,
                                   public content::RenderProcessHostObserver {
@@ skipping 70 matching lines @@
   // Track all observed render processes to un-observe them on exit.
   ScopedObserver<content::RenderProcessHost, SubprocessMetricsProvider>
       scoped_observer_;
 
   base::WeakPtrFactory<SubprocessMetricsProvider> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(SubprocessMetricsProvider);
 };
 
 #endif  // CHROME_BROWSER_METRICS_SUBPROCESS_METRICS_PROVIDER_H_