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 91214c179f9fb27051873c40a331821b3198386e..b71954d9411fe5eae0ba24adc5c43944ac8ee5f0 100644
--- a/net/http/http_cache.h
+++ b/net/http/http_cache.h
@@ -68,6 +68,8 @@ 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:
@@ -239,6 +241,8 @@ 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.