Add reverse dns lookup as a method on InternetAddress.

runtime/bin/socket_macos.cc

Index: runtime/bin/socket_macos.cc
diff --git a/runtime/bin/socket_macos.cc b/runtime/bin/socket_macos.cc
index 42f128c58d93e0c6c210b5561fcbbb49cd258e3b..a8cb7e0858aa805e81d17e19dfb6db7500459e41 100644
--- a/runtime/bin/socket_macos.cc
+++ b/runtime/bin/socket_macos.cc
@@ -221,6 +221,28 @@ AddressList<SocketAddress>* Socket::LookupAddress(const char* host,
 }
 
 
+const char* Socket::ReverseLookup(RawAddr addr, OSError** os_error) {
+  char* host = new char[NI_MAXHOST];
+  int status = TEMP_FAILURE_RETRY(getnameinfo(
+      &addr.addr,
+      SocketAddress::GetAddrLength(&addr),
+      host,
+      NI_MAXHOST,
+      NULL,
+      0,
+      NI_NAMEREQD));
+  if (status != 0) {
+    ASSERT(*os_error == NULL);
+    *os_error = new OSError(status,
+                            gai_strerror(status),
+                            OSError::kGetAddressInfo);
+    delete host;
+    return NULL;
+  }
+  return host;
+}
+
+
 static bool ShouldIncludeIfaAddrs(struct ifaddrs* ifa, int lookup_family) {
   int family = ifa->ifa_addr->sa_family;
   if (lookup_family == family) return true;