“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.” – Google.
To get started just visit http://code.google.com/webtoolkit/speedtracer/get-started.html
Tried to perform the trace on Yahoo! website and the result is below. Comparing this with HttpWatch (IE) or HttpFox (FF), Speed Tracer seems to focus more on what happen in the browser, while HttpWatch and HttpFox for focus on the request. Anyway, I still to play more to find out its power. But I believe this is useful for developers and testers.