components: Cleanup class/struct fwd declarations

components/history/core/browser/history_types.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 COMPONENTS_HISTORY_CORE_BROWSER_HISTORY_TYPES_H_
 #define COMPONENTS_HISTORY_CORE_BROWSER_HISTORY_TYPES_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 17 matching lines @@
 #include "components/query_parser/query_parser.h"
 #include "ui/base/page_transition_types.h"
 #include "ui/gfx/geometry/size.h"
 #include "url/gurl.h"
 
 namespace history {
 
 // Forward declaration for friend statements.
 class HistoryBackend;
 class PageUsageData;
-class URLDatabase;
 
 // Container for a list of URLs.
 typedef std::vector<GURL> RedirectList;
 
 typedef int64_t FaviconBitmapID;  // Identifier for a bitmap in a favicon.
 typedef int64_t SegmentID;        // URL segments for the most visited view.
 typedef int64_t IconMappingID;    // For page url and icon mapping.
 
 // The enumeration of all possible sources of visits is listed below.
 // The source will be propagated along with a URL or a visit item
@@ skipping 505 matching lines @@
   void SetTimeRangeForOneDay(base::Time time);
 
   std::set<GURL> urls;
   base::Time begin_time;
   base::Time end_time;
 };
 
 }  // namespace history
 
 #endif  // COMPONENTS_HISTORY_CORE_BROWSER_HISTORY_TYPES_H_