async_test(function () {
    var webpage = require('webpage');

    // NOTE: HTTP header names are case-insensitive. Our test server
    // returns the name in lowercase.

    var page = webpage.create();
    assert_type_of(page.customHeaders, 'object');
    assert_deep_equals(page.customHeaders, {});

    page.onResourceRequested = this.step_func(function(requestData, request) {
        assert_type_of(request.setHeader, 'function');
        request.setHeader('CustomHeader', 'CustomValue');
    });
    page.open(TEST_HTTP_BASE + 'echo', this.step_func_done(function (status) {
        var json, headers;
        assert_equals(status, 'success');
        json = JSON.parse(page.plainText);
        headers = json.headers;
        assert_own_property(headers, 'customheader');
        assert_equals(headers.customheader, 'CustomValue');
    }));

}, "add custom headers in onResourceRequested");