Bug 111644

[meta] RecalcStyle accounts for too much time on the main thread In previous of Telemetry using Chromium content_shell on an Android device, we see style recalc taking up as much as 24% of total mainthread time. https://docs.google.com/spreadsheet/ccc?key=0AlC4tS7Ao1fIdGtJTWlSaUItQ1hYaDFDcWkzeVAxOGc#gid=0 is a very run, but I will add more recent runs in further comments. This is a meta bug to track planned work of making this take up less main-thread time. I expect we will take several approaches, including: - Remove unnecessary recalcs (by deferring the work as much as possible) - Make parts of recalc faster (for example canShareStyleWith() is very very hot) - Explore radical ideas such as making style recalc resume-able (resolve only as much of the docuement as is needed to answer a specific query) or computable by parallel threads.