Summary:
React Native bundler (aka Metro Bundler) was splitted from the main codebase some time ago (now it lives [[https://github.com/facebook/metro-bundler|here]]). To make it more agnostic, polyfills will be moved out from it, so people who doesn't need them does not include them. However, RN will still need them, so the first step is to copy them back to RN so that we can provide them to Metro Bundler later.
We also include a way of passing the list of polyfills to include, as an `Array<string>`. The field is called `polyfills`, and defaults to the traditional list that is currently included in the package manager [see here](be1843cddc/packages/metro-bundler/src/defaults.js (L27-L37)).
In future commits, `metro-bundler` will be able to manage the `polyfills` array passed to it, and use it, instead of the pre-defined ones.
Reviewed By: davidaurelio
Differential Revision: D5381614
fbshipit-source-id: 749d536b781843ecb3067803e44398cd6df941f1
ad0fe15e2e