Added --disable-ipv4 and --disable-ipv6 switches. By default both enabled.

cloud_print/gcp20/prototype/dns_response_builder.cc

Index: cloud_print/gcp20/prototype/dns_response_builder.cc
diff --git a/cloud_print/gcp20/prototype/dns_response_builder.cc b/cloud_print/gcp20/prototype/dns_response_builder.cc
index 46f82cdb0a4ae7c8ae5fa65f5f3f2b5d4cdf7c80..07d07eaacf1fa54e6bd44ddcfd11e4748a6cfa17 100644
--- a/cloud_print/gcp20/prototype/dns_response_builder.cc
+++ b/cloud_print/gcp20/prototype/dns_response_builder.cc
@@ -81,7 +81,6 @@ void DnsResponseBuilder::AppendA(const std::string& service_domain_name,
   // TODO(maksymb): IP to send must depends on interface from where query was
   // received.
   if (http_ipv4.empty()) {
-    LOG(ERROR) << "Invalid IP";
     return;
   }
 
@@ -96,7 +95,6 @@ void DnsResponseBuilder::AppendAAAA(const std::string& service_domain_name,
   // TODO(maksymb): IP to send must depends on interface from where query was
   // received.
   if (http_ipv6.empty()) {
-    LOG(ERROR) << "Invalid IP";
     return;
   }