content: Cleanup class/struct forward declarations

content/common/indexed_db/indexed_db_key.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 CONTENT_COMMON_INDEXED_DB_INDEXED_DB_KEY_H_
 #define CONTENT_COMMON_INDEXED_DB_INDEXED_DB_KEY_H_
 
 #include <stddef.h>
 
 #include <string>
 #include <vector>
 
 #include "base/logging.h"
 #include "base/strings/string16.h"
 #include "content/common/content_export.h"
 #include "third_party/WebKit/public/platform/modules/indexeddb/WebIDBTypes.h"
 
-namespace blink {
-class WebIDBKey;
-}
-
 namespace content {
 
 class CONTENT_EXPORT IndexedDBKey {
  public:
   typedef std::vector<IndexedDBKey> KeyArray;
 
   IndexedDBKey();  // Defaults to blink::WebIDBKeyTypeInvalid.
   explicit IndexedDBKey(blink::WebIDBKeyType);  // must be Null or Invalid
   explicit IndexedDBKey(const KeyArray& array);
   explicit IndexedDBKey(const std::string& binary);
@@ skipping 44 matching lines @@
 
   size_t size_estimate_;
 };
 
 // An index id, and corresponding set of keys to insert.
 using IndexedDBIndexKeys = std::pair<int64_t, std::vector<IndexedDBKey>>;
 
 }  // namespace content
 
 #endif  // CONTENT_COMMON_INDEXED_DB_INDEXED_DB_KEY_H_