Remove dead code

chrome/browser/history/history_backend.h

Index: chrome/browser/history/history_backend.h
diff --git a/chrome/browser/history/history_backend.h b/chrome/browser/history/history_backend.h
index 41ff49f9e2052aee21600914a14d1468e7fda879..e0cafd17dd4f0828cd89b3771073091aa0a82e8f 100644
--- a/chrome/browser/history/history_backend.h
+++ b/chrome/browser/history/history_backend.h
@@ -15,33 +15,43 @@
 #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/android/android_history_types.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.