Adds a new class HttpCache::Writers for multiple cache transactions reading from the network.

net/http/http_cache.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.
 
 // This file declares a HttpTransactionFactory implementation that can be
 // layered on top of another HttpTransactionFactory to add HTTP caching.  The
 // caching logic follows RFC 7234 (any exceptions are called out in the code).
 //
 // The HttpCache takes a disk_cache::Backend as a parameter, and uses that for
 // the cache storage.
@@ skipping 228 matching lines @@
     kMetadataIndex,
 
     // Must remain at the end of the enum.
     kNumCacheEntryDataIndices
   };
 
   class MetadataWriter;
   class QuicServerInfoFactoryAdaptor;
   class Transaction;
   class WorkItem;
+  class Writers;
+  friend class WritersTest;  // To access ActiveEntry in the test class.
+  friend class MockHttpCacheTransaction;
   friend class Transaction;
   friend class ViewCacheHelper;
   struct PendingOp;  // Info for an entry under construction.
 
   // To help with testing.
   friend class MockHttpCache;
 
   using TransactionList = std::list<Transaction*>;
   using TransactionSet = std::unordered_set<Transaction*>;
   typedef std::list<std::unique_ptr<WorkItem>> WorkItemList;
@@ skipping 291 matching lines @@
   THREAD_CHECKER(thread_checker_);
 
   base::WeakPtrFactory<HttpCache> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(HttpCache);
 };
 
 }  // namespace net
 
 #endif  // NET_HTTP_HTTP_CACHE_H_