Web speed tracer

http://code.google.com/webtoolkit/speedtracer/get-started.html

Speed Tracer is a Google Chrome extension that helps you identify and fix performance problems in your web applications. It visualizes metrics that are taken from low level instrumentation points inside of the browser and analyzes them as your application runs. Using Speed Tracer you are able to get a better picture of where time is being spent in your application

don't forget to start chrome with this flag:

--enable-extension-timeline-api