Summary: This adds a build option for using Prepack (an experimental packager) to
build a bundle. It doesn't actually take on the npm package dependency
because it's not published/open source (yet).
This will be used while we experiment and should be maintained as the
build system changes so that we can continue getting fresh builds.
I found that saveBundleAndMap and processBundle were over abstracted and
got in my way so I inlined it and removed the unit tests because the unit
test was testing trivial code that is likely to change interface.
I went with a separate build phase and a separate Bundle class even though
there are a lot of commonalities. I imagine that the requirements for
Prepack will continue to diverge. Especially for source maps but a larger
refactor could try to unify these a bit more. The fact that modules are
wrapped before the write phase seems to be an unfortunate architecture
that makes this difficult.
Closes https://github.com/facebook/react-native/pull/4226
Reviewed By: amasad
Differential Revision: D2673760
Pulled By: sebmarkbage
fb-gh-sync-id: 299ccc42e4be1d9dee19ade443ea3388db2e39a8
43f18ffd08