[WIP] Turn on ADVANCED_OPTIMIZATIONS when compiling protobuf JS

[jjbubudi]

Fixes protocolbuffers/protobuf-javascript#92

After optimization the bundle size went from ~156KB to ~47KB (uncompressed)

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[jjbubudi]

I signed it!

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CLAs look good, thanks!

[jjbubudi]

jspb is available in the google-protobuf module. Exporting jspb here and subsequently using it in test will result in a lot of undefined symbol errors because the compiled google-protobuf is expecting obfuscated symbols.

[jjbubudi]

See comment above. We should use google-protobuf's jspb instead of the one we exported for tests.

[skyjia]

any updates on this PR?

[acozzette]

We are closing all open JavaScript pull requests because the JavaScript implementation is moving to a new repository: https://github.com/protocolbuffers/protobuf-javascript Sorry for the inconvenience but please feel free to reopen the pull request in the new repo.