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

net/http/http_cache.h

Index: net/http/http_cache.h
diff --git a/net/http/http_cache.h b/net/http/http_cache.h
index 635cb92d557d17c6c60ca459f4117deb075f71f7..6113bf1a2dca0c3dcf614673c3ebf8037e7a0a1d 100644
--- a/net/http/http_cache.h
+++ b/net/http/http_cache.h
@@ -69,6 +69,8 @@ class NET_EXPORT HttpCache : public HttpTransactionFactory,
     DISABLE
   };
 
+  class WritersTest;
+
   // A BackendFactory creates a backend object to be used by the HttpCache.
   class NET_EXPORT BackendFactory {
    public:
@@ -240,6 +242,8 @@ class NET_EXPORT HttpCache : public HttpTransactionFactory,
   class QuicServerInfoFactoryAdaptor;
   class Transaction;
   class WorkItem;
+  class Writers;
+  friend class WritersTest;  // To access ActiveEntry in the test class.
   friend class Transaction;
   friend class ViewCacheHelper;
   struct PendingOp;  // Info for an entry under construction.