Remove obviously unneeded forward declarations from headers under src/{app,base,net}.

net/disk_cache/storage_block.h

 // Copyright (c) 2010 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.
 
 // See net/disk_cache/disk_cache.h for the public interface.
 
 #ifndef NET_DISK_CACHE_STORAGE_BLOCK_H__
 #define NET_DISK_CACHE_STORAGE_BLOCK_H__
 #pragma once
 
 #include "net/disk_cache/addr.h"
 #include "net/disk_cache/mapped_file.h"
 
 namespace disk_cache {
 
-class EntryImpl;
-
 // This class encapsulates common behavior of a single "block" of data that is
 // stored on a block-file. It implements the FileBlock interface, so it can be
 // serialized directly to the backing file.
 // This object provides a memory buffer for the related data, and it can be used
 // to actually share that memory with another instance of the class.
 //
 // The following example shows how to share storage with another object:
 //    StorageBlock<TypeA> a(file, address);
 //    StorageBlock<TypeB> b(file, address);
 //    a.Load();
@@ skipping 57 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(StorageBlock);
 };
 
 typedef StorageBlock<EntryStore> CacheEntryBlock;
 typedef StorageBlock<RankingsNode> CacheRankingsBlock;
 
 }  // namespace disk_cache
 
 #endif  // NET_DISK_CACHE_STORAGE_BLOCK_H__