net: Add fuzzer for HostResolverImpl.

net/dns/dns_client.h

Index: net/dns/dns_client.h
diff --git a/net/dns/dns_client.h b/net/dns/dns_client.h
index 01d024b9a17032b18d51c57177e74ae478f1177a..684b8e62c5aa69ac9fdce25b161bb44cf6b2135d 100644
--- a/net/dns/dns_client.h
+++ b/net/dns/dns_client.h
@@ -8,10 +8,12 @@
 #include <memory>
 
 #include "net/base/net_export.h"
+#include "net/base/rand_callback.h"
 
 namespace net {
 
 class AddressSorter;
+class ClientSocketFactory;
 struct DnsConfig;
 class DnsTransactionFactory;
 class NetLog;
@@ -38,6 +40,14 @@ class NET_EXPORT DnsClient {
 
   // Creates default client.
   static std::unique_ptr<DnsClient> CreateClient(NetLog* net_log);
+
+  // Creates a client for testing.  Allows using a mock ClientSocketFactory and
+  // a deterministic "random" number generator. |socket_factory| must outlive
+  // the returned DnsClient.
+  static std::unique_ptr<DnsClient> CreateClientForTesting(
+      NetLog* net_log,
+      ClientSocketFactory* socket_factory,
+      const RandIntCallback& rand_int_callback);
 };
 
 }  // namespace net