How to enable print media emulation in headless Chrome?

In the latest (tip-of-tree) Chrome DevTools Protocol Viewer documentation under Emulation, there is a section about emulated media. This one line will enable print media emulation:

Emulation.setEmulatedMedia({media: "print"});

In addition, if the viewport width is set to that of an 8.5in sheet of paper (~816px @ 96 DPI), then the screenshot will resemble a color print preview.

const viewportWidth = 816;    // 8.5 inconst viewportHeight = 1056;  // 11 inconst deviceMetrics = {    width: viewportWidth,    height: viewportHeight,    deviceScaleFactor: 0,    mobile: false,    fitWindow: false};Emulation.setDeviceMetricsOverride(deviceMetrics);Emulation.setVisibleSize({width: viewportWidth, height: viewportHeight});

Figured out how to do this using in Django (python) with Selenium and Chromedriver.

    def set_media_emulation(self, media):        """            This is used to trigger between print mode and screen to allow            @media (print) css styles to take effect            call this in your testcase like self.set_media_emulation('print')            or self.set_media_emulation('screen')        :param media:        :return:        """        command_url = "/session/{session_id}/chromium/send_command".format(session_id=self.selenium.session_id)        self.selenium.command_executor._commands["send_command"] = ("POST", command_url)        params = {'cmd': 'Emulation.setEmulatedMedia', 'params': {'media': media}}        return self.selenium.execute("send_command", params)

Where self.selenium is

from selenium.webdriver import Chromeself.selenium = Chrome(desired_capabilities=desired_capabilities,                                           options=chrome_options,                                           service_args=['--verbose'],                                           service_log_path=self.selenium_log_path)

For anyone looking for this, I figured out how to do it for Rspec+capybara+selenium:

def enable_print_emulation  bridge = Capybara.current_session.driver.browser.send(:bridge)  path = "/session/#{bridge.session_id}/chromium/send_command"  bridge.http.call(:post, path, cmd: 'Emulation.setEmulatedMedia',                                params: {media: 'print'})end

Then just call this method in your spec!