Don't refetch a CSS chunk if it's inlined into the HTML <head> #53
Description
In Gatsby v2, we'll be using webpack 4 and mini-css-extract-plugin. Gatsby tries to always inline the critical CSS for a page — which aligns perfectly with mini-css-extract-plugin's goals. Currently, however, if we inline a CSS chunk, it'll still be loaded once the webpack runtime loads in the client. Discussing this with @sokra, he suggested that we'd adopt a convention where if you add a data-href to the <style> tag that then webpack wouldn't reload the inlined css.