Add reverse dns lookup as a method on InternetAddress.

runtime/bin/socket_android.cc

Index: runtime/bin/socket_android.cc
diff --git a/runtime/bin/socket_android.cc b/runtime/bin/socket_android.cc
index 0aa5968eb5d00eec57bfc8161b0a1895f8eb4018..c08aeddeb57c329d0b93d8459f039e73b889c58c 100644
--- a/runtime/bin/socket_android.cc
+++ b/runtime/bin/socket_android.cc
@@ -222,6 +222,28 @@ 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;