[route]

Closes #278.

window_size: nil made Cuprite raise Ferrum::BrowserError: Invalid parameters on every page. Ferrum already leaves out --window-size when the size is nil, but Page#prepare_page always called resize(width: nil, height: nil), and Chrome rejects Browser.setWindowBounds without a size.

Now Cuprite resizes only when a size is set. Otherwise it applies just the viewport settings, so mobile: and scale_factor: still work. Chrome keeps its own window size, which makes start-maximized usable:

Capybara::Cuprite::Driver.new(app, headless: false, window_size: nil, browser_options: { "start-maximized" => nil })

Verified in headful Chrome on a 2560×1440 screen: with start-maximized alone the window stays 1024×768 (normal), while with window_size: nil it opens at 2560×1410 (maximized).