Fix dart2js by copying keys of a map that is modified under us.

tests/standalone/standalone.status

Index: tests/standalone/standalone.status
diff --git a/tests/standalone/standalone.status b/tests/standalone/standalone.status
index 825bda7c00be5a40d7f30ca5c9c6ca38d11ee02e..ecdf02e3653ce8a348814442ad0564938c06b8cb 100644
--- a/tests/standalone/standalone.status
+++ b/tests/standalone/standalone.status
@@ -101,8 +101,6 @@ float_array_test: Skip # This is a VM test
 int_array_test: Skip  # This is a VM test
 medium_integer_test: Fail, OK # Test fails with JS number semantics: issue 1533.
 io/process_exit_negative_test: Fail, OK # relies on a static error that is a warning now.
-io/http_server_handler_test: Fail # Issue 7739.
-io/http_server_early_client_close_test: Fail, Pass # Issue 7739 (passes in checked mode).
 package/package_isolate_test: Skip # spawnUri does not work in dart2js. See issue 3051
 debugger/*: Skip # Do not run standalone vm debugger tests with dart2js.