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

net/http/http_cache_lookup_manager_unittest.cc

 // Copyright (c) 2016 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.
 
 #include <string>
 
 #include "base/memory/ptr_util.h"
 #include "base/run_loop.h"
 #include "net/base/net_errors.h"
 #include "net/base/test_completion_callback.h"
@@ skipping 46 matching lines @@
   int rv = cache->CreateTransaction(DEFAULT_PRIORITY, &trans);
   EXPECT_THAT(rv, IsOk());
   ASSERT_TRUE(trans.get());
 
   rv = trans->Start(&request, callback.callback(), NetLogWithSource());
   base::RunLoop().RunUntilIdle();
 
   if (rv == ERR_IO_PENDING)
     rv = callback.WaitForResult();
 
-  ASSERT_EQ(mock_trans->return_code, rv);
+  ASSERT_EQ(mock_trans->start_return_code, rv);
   if (OK != rv)
     return;
 
   const HttpResponseInfo* response = trans->GetResponseInfo();
   ASSERT_TRUE(response);
 
   std::string content;
   rv = ReadTransaction(trans.get(), &content);
 
   EXPECT_THAT(rv, IsOk());
@@ skipping 196 matching lines @@
 
   base::RunLoop().RunUntilIdle();
   // Make sure no new net layer transaction is created.
   EXPECT_EQ(1, mock_cache.network_layer()->transaction_count());
   EXPECT_EQ(2, mock_cache.disk_cache()->open_count());
   EXPECT_EQ(1, mock_cache.disk_cache()->create_count());
   RemoveMockTransaction(mock_trans3.get());
 }
 
 }  // namespace net