[This documentation is preliminary and is subject to change.]
Outputs a timestamp to the Console based on how long the current browser tab has been open. If used while a UI Responsiveness profiling session is recording, it will also create a user mark in the session timeline similar to a performance.mark.
If a string is submitted as the first parameter, it will be used as a label for the console output and the user mark. If a numeric value is submitted, it is cast to a string and used as a label.