Node.js中的“CrankShaftScript”是什么?

There are more and more references in the Node.js community to "CrankShaftScript" (and "CrankShaftJS") on Twitter, GitHub, and Facebook group discussions. I thought Node.js was written in C++ and JavaScript, so what is CrankShaftScript referring to in performance regression bugs like this one:There are more and more references in the Node.