The user-agent string used by WebKit. Unusual user-agent strings may cause web content to render incorrectly or fail to run, as many web pages are written to parse the user-agent strings of only the most popular browsers. Therefore, it's typically better to not completely override the standard user-agent, but to use webkit.settings.Settings.setUserAgentWithApplicationDetails instead.
If this property is set to the empty string or null, it will revert to the standard user-agent.
Builder instance for fluent chaining
Set userAgent property.