Summary:
`metro-bundler` v0.21 contains a rewritten bundling mechanism, with simplified logic and much faster rebuild times, called delta bundler. This release contains a couple of breaking changes:
* Now, when using a custom transformer, the list of additional babel plugins to apply are passed to the `transform()` method. These are used in non-dev mode for optimization purposes (Check 367a5f5db8 (diff-40653f0c822ac59a5af13d5b4ab31d84) to see how to handle them from the transformer).
* Now, when using a custom transformer outputting `rawMappings`, the transformer does not need to call the `compactMappings` method before returning (check d74685fd1d (diff-40653f0c822ac59a5af13d5b4ab31d84) for more info).
* We've removed support for two config parameters: `postProcessModules` and `postProcessBundleSourcemap`.
Reviewed By: davidaurelio
Differential Revision: D6186035
fbshipit-source-id: 242c5c2a954c6b9b6f339d345f888eaa44704579
Rafael Oleza