Remove dead code

chrome/browser/history/history_backend.h

 // Copyright (c) 2012 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_HISTORY_HISTORY_BACKEND_H_
 #define CHROME_BROWSER_HISTORY_HISTORY_BACKEND_H_
 
 #include <set>
 #include <string>
 #include <utility>
 #include <vector>
 
 #include "base/containers/mru_cache.h"
 #include "base/files/file_path.h"
 #include "base/gtest_prod_util.h"
 #include "base/memory/memory_pressure_listener.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/single_thread_task_runner.h"
 #include "base/task/cancelable_task_tracker.h"
 #include "chrome/browser/history/expire_history_backend.h"
 #include "chrome/browser/history/history_database.h"
-#include "chrome/browser/history/history_marshaling.h"
 #include "chrome/browser/history/history_types.h"
 #include "chrome/browser/history/thumbnail_database.h"
 #include "chrome/browser/history/visit_tracker.h"
 #include "components/history/core/browser/keyword_id.h"
+#include "components/visitedlink/browser/visitedlink_delegate.h"
 #include "sql/init_status.h"
 
+#if defined(OS_ANDROID)
+#include "chrome/browser/history/history_marshaling_android.h"
+#endif
+
+class HistoryURLProvider;
+struct HistoryURLProviderParams;
+struct ImportedFaviconUsage;
 class TestingProfile;
-class TypedUrlSyncableService;
 struct ThumbnailScore;
 
+namespace base {
+class MessageLoop;
+}
+
 namespace history {
 #if defined(OS_ANDROID)
 class AndroidProviderBackend;
 #endif
 
 class CommitLaterTask;
+struct DownloadRow;
 class HistoryClient;
+class HistoryDBTask;
+class InMemoryHistoryBackend;
 class VisitFilter;
-struct DownloadRow;
+class TypedUrlSyncableService;
 
 // The maximum number of icons URLs per page which can be stored in the
 // thumbnail database.
 static const size_t kMaxFaviconsPerPage = 8;
 
 // The maximum number of bitmaps for a single icon URL which can be stored in
 // the thumbnail database.
 static const size_t kMaxFaviconBitmapsPerIconURL = 8;
 
 class QueuedHistoryDBTask {
@@ skipping 802 matching lines @@
 
   // Listens for the system being under memory pressure.
   scoped_ptr<base::MemoryPressureListener> memory_pressure_listener_;
 
   DISALLOW_COPY_AND_ASSIGN(HistoryBackend);
 };
 
 }  // namespace history
 
 #endif  // CHROME_BROWSER_HISTORY_HISTORY_BACKEND_H_