Stub out Socket::LookAddress on Fuchsia

runtime/bin/socket_fuchsia.cc

Index: runtime/bin/socket_fuchsia.cc
diff --git a/runtime/bin/socket_fuchsia.cc b/runtime/bin/socket_fuchsia.cc
index b79d1c0956b6d2df588dbe7f453cb35af908a015..b3935eb9091d299c48d7550cae0812ea635bd4e3 100644
--- a/runtime/bin/socket_fuchsia.cc
+++ b/runtime/bin/socket_fuchsia.cc
@@ -115,7 +115,12 @@ intptr_t Socket::GetStdioHandle(intptr_t num) {
 AddressList<SocketAddress>* Socket::LookupAddress(const char* host,
                                                   int type,
                                                   OSError** os_error) {
-  UNIMPLEMENTED();
+  // UNIMPLEMENTED
+  ASSERT(*os_error == NULL);
+  *os_error = new OSError(-1,
+                          "Socket::LookupAddress not implemented in "
+                          "Fuchsia Dart VM runtime",
+                          OSError::kGetAddressInfo);
   return NULL;
 }