This is a blog post quote from other people, but want to put it here as self reference in the future and in the hope that it will help more people.
There have been some great app performance resources surfacing recently, so I thought it would make sense to do a roundup.
I've recently seen apps whose performance is being crushed by large & expensive paints, extra layouts, bad event decoupling or too many network requests. They are all fixable items, and Chrome's DevTools and tracing tool both do a great job of showing you what's going on under the hood.
Web Performance Power Tool: HTTP Archive (HAR)
A rundown of the HAR file and how you can use it to diagnose the network side of your application, with +Ilya Grigorik and +Peter Lubbers.
Video: Make The Web Fast - The HAR Show: Capturing and Analyzing performance data with HTTP Archive format
Wait, DevTools could do THAT?
A fantastic presentation by +Ilya Grigorik on Chrome's DevTools
Progressive jpegs: a new best practice
Ann Robson explains how we can all reduce our apps' bandwidth consumption by making use of progressive jpegs
+John McCutchan and +Ilya Grigorik (he keeps showing up this guy!) cover Chrome's tracing tool. If you're a power user, this one is a must.
Snow in canvas land
+Jake Archibald relives the horror of his 2-year-old code, and sets about fixing it
Improving Web App Performance With the Chrome DevTools Timeline and Profiles
A very thorough tutorial (with ANIMATED GIFS!) by +Addy Osmani on how to use Chrome DevTools to diagnose memory and performance issues.
Scrolling Performance and Parallaxin'
Two articles by yours truly on understanding and improving scrolling performance in your applications
Google I/O 2012 - Jank Busters: Building Performant Web Apps
+Nat Duca and +Tom Wiltzius of Google's Chrome GPU team cover a host of tips & tricks for maximizing your app's rendering performance
Why moving elements with translate() is better than pos:abs top/left
+Paul Irish on using translates vs absolute positioning, and the performance implications of both