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

tests/standalone/standalone.status

 # Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 package/invalid_uri_test: Fail, OK # Fails intentionally
 
 # These tests fail because the test scripts do not use the new streams library.
 # When the test scripts are updated, and the precompiled dart executable is
 # updated, they will be re-enabled.  Issue 7724.
 io/test_runner_test: Pass, Fail
@@ skipping 83 matching lines @@
 [ $arch == simarm ]
 *: Skip
 
 [ $compiler == dart2js ]
 number_identity_test: Skip # Bigints and int/double diff. not supported.
 typed_array_test: Skip # This is a VM test
 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.
 
 [ $compiler == dart2js && $jscl ]
 assert_test: Fail, OK # Assumes unspecified fields on the AssertionError.
 byte_array_test: Fail, OK # ByteArray
 deoptimization_test: Fail, OK # Requires bigint.
 out_of_memory_test: Fail, OK # d8 handles much larger arrays than Dart VM.
 io/http_parser_test: Fail, OK # ByteArray
 io/options_test: Fail, OK # Cannot pass options to d8.
 
 [ $compiler == dart2js && $runtime == none ]
 io/options_test: Fail
 medium_integer_test: Pass # The test only fails at runtime, not at compilation.
 
 [ $compiler == dart2js && $browser ]
 *: Skip
 
 [ $compiler == dart2js && $checked ]
 io/http_read_test: Skip # Timeout TODO(ngeoffray): investigate
 io/list_input_stream_test: Skip # Timeout TODO(ngeoffray): investigate
 
 [ $compiler == dart2dart ]
 # Skip until we stabilize language tests.
 *: Skip